PART II. NEW DATA._Sex-linked Inheritance in Drosophila

WHITE.

(Plate II, figure 11.)

The recessive character white eye-color, which appeared in May 1910, was

the first sex-linked mutation in _Drosophila_ (Morgan, 1910_a_, 1910_b_).

Soon afterwards (June 1910) rudimentary appeared, and the two types were

crossed (Morgan, 1910_c_). Under the conditions of culture the viability of

rudimentary was extremely poor, but the data demonstrated the occurrence of

recombination of the factors in the ovogenesis so that white and

rudimentary, though both sex-linked, were brought together into the same

individual. The results were not fully recognized as linkage, because white

and rudimentary are so far apart in the chromosome that they seemed to

assort freely from each other.

Owing to the excellent viability and the perfect sharpness of separation,

white was extensively used in linkage experiments, especially with

miniature and yellow (Morgan, 1911_a_; Morgan and Cattell, 1912 and 1913).

White has been more extensively used than any other character in

_Drosophila_, though it is now being used very little because of the fact

that the double recessives of white with other sex-linked eye-colors, such

as vermilion, are white, and consequently a separation into the true

genetic classes is impossible. The place of white has been taken by eosin,

which is an allelomorph of white and which can be readily used with any

other eye-color.

The locus of white and its allelomorphs is only 1.1 units from that of

yellow, which is the zero of the chromosome. Yellow and white are very

closely linked, therefore giving only about one cross-over per 100 flies.

All the published data upon the linkage of white with other sex-linked

characters have been collected into table 65.

RUDIMENTARY.

Rudimentary, which appeared in June 1910, was the second sex-linked

character in _Drosophila_ (Morgan, 1910_c_). Its viability has always been

very poor; in this respect it is one of the very poorest of the sex-linked

characters. The early linkage data (Morgan, 1911_a_) derived from mass

cultures have all been discarded. By breeding from a single F_1 female in

each large culture bottle it has been possible to obtain results which are

fairly trustworthy (Morgan, 1912_g_; Morgan and Tice, 1914). These data

appear in table 65, which summarizes all the published data. {26}

The locus of rudimentary is at 55.1, for a long time the extreme right end

of the known chromosome, though recently several mutants have been found to

lie somewhat beyond it.

[Illustration: Fig. A. _a._ rudimentary wing; _b._ the wild fly for

comparison.]

The rudimentary males are perfectly fertile, but the rudimentary females

rarely produce any offspring at all, and then only a very few. The reason

for this is that most of the germ-cells cease their development in the

early growth stage of the eggs (Morgan, 1915_a_).

MINIATURE.

(Plate II. figures 7 and 8.)

The recessive sex-linked mutant miniature wings appeared in August 1910

(Morgan, 1911b and 1912a). The viability of miniature is fair, and this

stock has been used in linkage experiments more than any {27} other, with

the single exception of white. While the wings of miniature usually extend

backwards, they are sometimes held out at right angles to the body, and

especially in acid bottles the miniature flies easily become stuck to the

food or the wings become stringy, so that other wing characters are not

easy to distinguish in those flies which are also miniature. At present

vermilion, whose locus is at 33, in being used more frequently in linkage

work. The locus of miniature at 36.1 is slightly beyond the middle of the

chromosome.

VERMILION.

(Plate II. figure 10.)

The recessive sex-linked mutant vermilion eye-color (Morgan, 1911_c_ and

1912_a_) appeared in November 1910, and has appeared at least twice since

then (Morgan and Plough, 1915). This is one of the best of the sex-linked

characters, on account of its excellent viability, its sharp distinction

from normal with very little variability, its value as a double recessive

in combination with other sex-linked eye-colors, and because of its

location at 33.0, very near to the middle of the known chromosome.

YELLOW.

(Plate I. figure 5.)

The recessive sex-linked mutant yellow body and wing-color appeared in

January 1911 (Morgan, 1911_c_ and 1912_a_). Its first appearance was in

black stock; hence the fly was a double recessive, then called brown. Later

the same mutation has appeared independently from gray stock. Yellow was

found to be at the end of the X chromosome, and this end was arbitrarily

chosen as the zero or the "left end," while the other gens are spoken of as

lying at various distances to the right of yellow. Recently a lethal gen

has been located less than one-tenth of a unit (-0.04) to the left of

yellow, but yellow is still retained as the zero-point.

The viability of yellow is fairly good and the character can be separated

from gray with great facility, and in consequence yellow has been used

extensively, although at present it is being used less than formerly, since

eosin lies only 1.1 units distant from yellow and is generally preferred.

ABNORMAL ABDOMEN.

(Plate I. figure 4.)

The dominant sex-linked character abnormal abdomen appeared in July 1911

(Morgan, 1911_d_). It was soon found that the realization of the abnormal

condition depended greatly upon the nature of the environment (Morgan,

1912). Recently a very extensive study of this character has been published

(Morgan, 1915). As this case has been reviewed in the introduction, there

is little further to be said here. {28} Because of the change that takes

place as the culture grows older (the abnormal changing to normal), this

character is not of much value in linkage work. The location of the factor

in the X chromosome at 2.4 has been made out from the data given by Morgan

(1915_b_). These data, which in general include only the abnormal classes,

are summarized in table 1.

TABLE 1.--_Linkage data, from Morgan, 1915b._

+------------------+-----------+-----------+------------+

+------------------+-----------+-----------+------------+

| Yellow white | 28,018 | 334 | 1.2 |

| Yellow abnormal | 15,314 | 299 | 2.0 |

| White abnormal | 16,300 | 277 | 1.7 |

+------------------+-----------+-----------+------------+

EOSIN.

(Plate II, figures 7 and 8.)

The recessive sex-linked mutation eosin eye-color appeared in August 1911

in a culture of white-eyed flies (Morgan 1912_a_). The eye-color is

different in the male and female, the male being a light pinkish yellow,

while the female is a rather dark yellowish pink. Eosin is allelomorphic to

white and the white-eosin compound or heterozygote has the color of the

eosin male. There is probably no special significance in this coincidence

of color, since similar dilutions to various degrees have been demonstrated

for all the other eye-colors tested (Morgan and Bridges, 1913). Since eosin

is allelomorphic to white, its locus is also at 1.1. Eosin is the most

useful character among all those in the left end of the chromosome.

BIFID.

The sex-linked wing mutant bifid, which appeared in November 1911, is

characterized by the fusion of all the longitudinal veins into a heavy

stalk at the base of the wing. The wing stands out from the body at a wide

angle, so that the fusion is easily seen. At the tip of the wing the third

longitudinal vein spreads out into a delta which reaches to the marginal

vein. The fourth longitudinal vein reaches the margin only rarely. There is

very often opposite this vein a great bay in the margin, or the whole wing

is irregularly truncated.

The stock of bifid was at first extremely varied in the amount of this

truncation. By selection a stock was secured which showed only very greatly

reduced wings like those shown in figures _a_, b. Another stock (figs. _c_,

_d_) was secured by outcrossing and selection which showed wings of nearly

normal size and shape, which always had the bifid stalk, generally the

spread positions (not as extreme), and often the delta and the shortened

fourth longitudinal vein. We believe that the extreme reduction in size

seen in the one stock was due to an added modifier of {29} the nature of

beaded, since this could be eliminated by outcrossing and selection.

[Illustration: FIG. B.--Bifid wing. _c_ and _d_ show the typical condition

of bifid wings. All the longitudinal veins are fused into a heavy stalk at

the base of the wing. _a_ shows the typical position in which the bifid

wings are held. The small size of the wings in _a_ and _b_ is due to the

action of a modifier of the nature of "beaded" which has been eliminated in

_c_, d.]

LINKAGE OF BIFID WITH YELLOW, WITH WHITE, AND WITH VERMILION.

The stock of the normal (not-beaded) bifid was used by Dr. R. Chambers,

Jr., for determining the chromosome locus of bifid by means of its linkage

relations to vermilion, white, and yellow (Chambers, 1913). We have

attempted to bring together in table 2 the complete data and to calculate

the locus of bifid.

TABLE 2.--_Linkage data, from Chambers, 1913._

+-----------------+------------+-------------+--------------+

+-----------------+------------+-------------+--------------+

| Yellow bifid | 3,175 | 182 | 5.8 |

| White bifid | 20,800 | 1,127 | 5.3 |

| Bifid vermilion | 2,509 | 806 | 32.1 |

+-----------------+------------+-------------+--------------+

{30}

In the crosses between white and bifid there were 1,127 cross-overs in a

total of 20,800 available individuals, which gives a cross-over value of

5.3. In the crosses between yellow and bifid there were 182 cross-overs in

a total of 3,175 available individuals, which gives a cross-over value of

5.8. In crosses between bifid and vermilion there were 806 cross-overs in a

total of 2,509, which gives a cross-over value of 32.1. On the basis of all

the data summarized in table 65, bifid is located at 6.3 to the right of

yellow.

LINKAGE OF CHERRY, BIFID, AND VERMILION.

In a small experiment of our own, three factors were involved--cherry,

bifid, and vermilion. A cherry vermilion female was crossed to a bifid

male. Two daughters were back-crossed singly to white bifid males. The

female offspring will then give data for the linkage of cherry white with

bifid, while the sons will show the linkage of the three gens, cherry,

bifid, and vermilion. The results are shown in table 3.

TABLE 3.--_P_1 cherry vermilion [female] [female] x bifid [male] [male]. B.

C.[2] F_1 wild-type [female] x white bifid [male] [male]._

|-----------------------------------

| | F_2 females. |

| |---------------------------+

| | |

|Refer-| Non-cross- |Cross-overs. |

|ence. | overs. | |

| |-------------+-------------+

|------+------+------+------+------+

| 262 | 40 | 46 | 1 | 2 |

| 263 | 47 | 45 | 3 | 3 |

| |------+------+------+------+

|Total.| 87 | 91 | 4 | 5 |

|-----------------------------------

|----------------------------------------------------------------------|

| | F_2 males. |

| |-----------------------------+---------------------------------|

| | w^c v | w^c b | w^c | w^c b_i v |

|Refer-| ------------ | ---+-------- | ---------+--- | ---+-----+--- |

|ence. | b_i | v | b_i v | |

| |--------------+--------------+---------------+-----------------|

~ | ver- | |bifid.|milion.| | ver- | bifid |type. |

|------+-------+------+------+-------+-------+-------+----------+------|

| 262 | 45 | 38 | 3 | 2 | 11 | 13 | .. | .. |

| 263 | 30 | 50 | 1 | 3 | 8 | 10 | 1 | .. |

| |-------+------+------+-------+-------+-------+----------+------|

|Total.| 75 | 88 | 4 | 5 | 19 | 23 | 1 | 0 |

|----------------------------------------------------------------------|

Both males and females give a cross-over value of 5 units for cherry bifid,

which is the value determined by Chambers. The order of the factors, viz,

cherry, bifid, vermilion, is established by taking advantage of the double

cross-over classes in the males. The male classes give a cross-over value

of 20 for bifid vermilion and 24 for cherry vermilion, which are low

compared with values given by other experiments. The locus of bifid at 6.3

is convenient for many linkage problems, but this advantage is largely

offset by the liability of the bifid flies to become stuck in the food and

against the sides of the bottle. Bifid flies can be separated from the

normal with certainty and with great ease. {31}

REDUPLICATED LEGS.

In November 1912 Miss Mildred Hoge found that a certain stock was giving

some males whose legs were reduplicated, either completely or only with

respect to the terminal segments (described and figured, Hoge, 1915).

Subsequent work by Miss Hoge showed that the condition was due to a

sex-linked gen, but that at room temperature not all the flies that were

genetically reduplicated showed reduplication. However, if the flies were

raised through the pupa stage in the ice-box at a temperature of about

10deg to 12deg a majority of the flies which were expected to show

reduplication did so. The most extremely reduplicated individual showed

parts of 14 legs.

In studying the cross-over values of reduplicated, only those flies that

have abnormal legs are to be used in calculation, as in the case of

abnormal abdomen where the phenotypically normal individuals are partly

genetically abnormal. Table 4 gives a summary of the data secured by Miss

Hoge.

TABLE 4.--_Summary of linkage data upon reduplicated legs, from Hoge,

1915._

+---------------------------+---------+---------+------------+

|---------------------------+---------+---------|------------|

| | | | |

|White reduplicated | 418 | 121 | 29.0 |

|Reduplicated vermilion | 667 | 11 | 1.7 |

|Reduplicated bar | 583 | 120 | 20.6 |

| | | | |

+---------------------------+---------+---------+------------+

The most accurate data, those upon the value for reduplicated and

vermilion, give for reduplicated a distance of 1.7 from vermilion, either

to the right or to the left. The distance from white is 29, which would

place the locus for reduplication to the left of vermilion, which is at 33.

The data for bar give a distance of 21, but since bar is itself 24 units

from vermilion, this distance of 21 would seem to place the locus to the

right of vermilion. The evidence is slightly in favor of this position to

the right of vermilion at 34.7, where reduplicated may be located

provisionally. In any case the locus is so near to that of vermilion that

final decision must come from data involving double crossing-over, _i. e._,

from a three-locus experiment.

LETHAL 1.

In February 1912 Miss E. Rawls found that certain females from a wild stock

were giving only about half as many sons as daughters. Tests continuing

through five generations showed that the sons that appeared were entirely

normal, but that half of the daughters gave again 2 : 1 sex-ratios, while

the other half gave normal 1 : 1 sex-ratios. {32}

The explanation of this mode of transmission became clear when it was found

that the cause of the death of half of the males was a particular factor

that had as definite a locus in the X chromosome as have other sex-linked

factors (Morgan, 1912_e_). Morgan mated females (from the stock sent to him

by Miss Rawls) to white-eyed males. Half of the females, as expected, gave

2 : 1 sex-ratios, and daughters from these were again mated to white males.

Here once more half of the daughters gave 2 : 1 sex-ratios, but in such

cases the sons were nearly all white-eyed and only rarely a red-eyed son

appeared, when under ordinary circumstances there should be just as many

red sons as white sons. The total output for 11 such females was as follows

(Morgan, 1914_b_): white [female], 457; red [female], 433; white [male],

370; red [male], 2. It is evident from these data that there must be

present in the sex-chromosome a gen that causes the death of every male

that receives this chromosome, and that this lethal factor lies very close

to the factor for white eyes. The linkage of this lethal (now called lethal

1) to various other sex-linked gens was determined (Morgan 1914_b_), and is

summarized in table 5. On the basis of these data it is found that the gen

lethal 1 lies 0.4 unit to the left of white, or at 0.7.

TABLE 5.--_Summary of linkage data upon lethal 1, from Morgan, 1914b, pp.

81-92._

+------------------------+---------+--------+-------------+

+------------------------+---------+--------+-------------+

| | | | |

| Yellow lethal 1 | 131 | 1 | 0.8 |

| Yellow miniature | 131 | 45 | 34.4 |

| Lethal 1 white | 1,763 | 7 | 0.4 |

| Lethal 1 miniature | 814 | 323 | 39.7 |

| White miniature | 994 | 397 | 39.9 |

| | | | |

+------------------------+---------+--------+-------------+

LETHAL 1a.

In the second generation of the flies bred by Miss Rawls, one female gave

(March 1912) only 3 sons, although she gave 312 daughters. It was not known

for some time (see lethals 3 and 3_a_) what was the cause of this extreme

rarity of sons. It is now apparent, however, that this mother carried

lethal 1 in one X and in the other X a new lethal which had arisen by

mutation. The new lethal was very close to lethal 1, as shown by the rarity

of the surviving sons, which are cross-overs between lethal 1 and the new

lethal that we may call lethal 1a. There is another class of cross-overs,

namely, those which have lethal 1 and get lethal 1_a_ by crossing-over.

These doubly lethal males must also die, but since they are theoretically

as numerous as the males (3) free from both lethals, we must double this

number (3 x 2) to get the total number of cross-overs. There were 312

daughters, but as the sons are normally about 96 per cent of the number of

the females, {33} we may take 300 as the number of the males which died.

There must have been, then, about 2 per cent of crossing-over, which makes

lethal 1_a_ lie about 2 units from lethal 1. This location of lethal 1_a_

is confirmed by a test that Miss Rawls made of the daughters of the

high-ratio female. Out of 98 of these daughters none repeated the high

sex-ratio and only 2 gave 1 [female] : 1 [male] ratios. The two daughters

which gave 1 : 1 ratios are cross-overs. There should be an equal number of

cross-overs which contain both lethals. These latter would not be

distinguishable from the non-cross-over females, each of which carries one

or the other lethal. In calculation, allowance can be made for them by

doubling the number of observed cross-overs (2 x 2) and taking 98 - 2 as

the number of non-cross-overs. The cross-over fraction {6 + 4}/{300 + 96}

gives 2.6 as the distance between the two lethals. Lethal 1_a_ is probably

to the right of lethal 1 at 0.7 + 2.6 = 3.3.

SPOT.

(Plate II, figures 14 to 17.)

In April 1912 there was found in the stock of yellow flies a male that

differed from yellow in that it had a conspicuous light spot on the upper

surface of the abdomen (Morgan, 1914_a_). In yellow flies this region is

dark brown in color. In crosses with wild flies the spot remained with the

yellow, and although some 30,000 flies were raised, none of the gray

offspring showed the spot, which should have occurred had crossing-over

taken place. The most probable interpretation of spot is that it was due to

another mutation in the yellow factor, the first mutation being from gray

to yellow and the second from yellow to spot.

Spot behaves as an allelomorph to yellow in all crosses where the two are

involved and is completely recessive to yellow, _i. e._, the yellow-spot

hybrid is exactly like yellow. A yellow-spot female, back-crossed to a spot

male, produces yellows and spots in equal numbers.

In a cross of spot to black it was found that the double recessive, spot

black, flies that appear in F_2 have, in addition to the spot on the

abdomen, another spot on the scutellum and a light streak on the thorax.

These two latter characters ("dot and dash") are very sharply marked and

conspicuous when the flies are young, but they are only juvenile characters

and disappear as the flies become older. The spot flies never show the "dot

and dash" clearly, and it only comes out when black acts as a developer.

These characters furnish a good illustration of the fact that mutant gens

ordinarily affect many parts of the body, though these secondary effects

often pass unnoticed.

In the F_2 of the cross of spot by black one yellow black fly appeared,

although none are expected, on the assumption that spot and yellow {34} are

allelomorphic. Unless due to crossing-over it must have been a mutation

from spot back to yellow. Improbable as this may seem to those who look

upon mutations as due to losses from the germ-plasm, yet we have records of

several other cases where similar mutations "backwards" have taken place,

notably in the case of eosin to white, under conditions where the

alternative interpretation of crossing-over is excluded.

SABLE.

(Plate I, figure 2.)

In an experiment involving black body-color[3] a fly appeared (July 19,

1912) whose body-color differed slightly from ordinary black in that the

trident mark on the thorax was sharper and the color itself was brighter

and clearer. This fly, a male, was mated to black females and gave some

black males and females, but also some gray (wild body-color) males and

females, showing not only that he was heterozygous for ordinary recessive

black, but at the same time that his dark color must be due to another kind

of black. The gray F_1 flies when mated together gave a series of gray and

dark flies in F_2 about as follows: In the females 3 grays to 1 dark; in

the males 3 grays to 5 dark in color. The result indicated that the new

black color, which we call sable, was due to a sex-linked factor. It was

difficult to discover which of the heterogeneous F_2 males were the new

blacks. Suspected males were bred (singly) to wild females, and the F_2

dark males, from those cultures that gave the closest approach to a 2 gray

[female] : 1 gray [male] : 1 dark [male], were bred to their sisters in

pairs in order to obtain sable females and males. Thus stock homozygous for

sable but still containing black as an impurity was obtained. It became

necessary to free it from black by successive individual out-crossings to

wild flies and extractions.

This account of how sable was purified shows how difficult it is to

separate two recessive factors that give closely similar somatic effects.

If a character like sable should be present in any other black stock, or if

a character like black should be present in sable, very erratic results

would be obtained if such stocks were used in experiments, before such a

population had been separated into its component races.

Sable males of the purified stock were mated to wild females and gave

wild-type (gray) males and females. These inbred gave the results shown in

table 6.

No sable females appeared in F_2, as seen in table 6. The reciprocal cross

gave the results shown in table 7.

{35}

The F_1 males were sable like their mother. The evidence thus shows that

sable is a sex-linked recessive character. Our next step was to determine

the linkage relations of sable to certain other sex-linked gens, namely,

yellow, eosin, cherry, vermilion, miniature, and bar.

TABLE 6.--_P_1 wild [female] [female] x sable [male]. F_1 wild-type

[female] [female] x F_1 wild-type [male] [male]._

+---------------+-------------------+-------------------+---------------+

| | | | |

| | | | |

+---------------+-------------------+-------------------+---------------+

| | | | |

| 88 C | 218 | 100 | 70 |

| 143 C | 245 | 108 | 72 |

| 146 C | 200 | 115 | 82 |

| +-------------------+-------------------+---------------+

| Total | 663 | 323 | 224 |

| | | | |

+---------------+-------------------+-------------------+---------------+

TABLE 7.--_P_1 sable [female] x wild [male] [male]. F_1 wild-type [female]

x F_1 sable [male]._

+--------------+-------------+-------------+-------------+-------------+

| | | | | |

+--------------+-------------+-------------+-------------+-------------+

| | | | | |

| 4 I | 10 | 10 | 6 | 10 |

| | | | | |

+--------------+-------------+-------------+-------------+-------------+

LINKAGE OF YELLOW AND SABLE.

The factor for yellow body-color lies at one end of the known series of

sex-linked gens. As already stated, we speak of this end as the left end of

the diagram, and yellow as the zero in locating factors.

When yellow (not-sable) females were mated to (not-yellow) sable males they

gave wild-type (gray) daughters and yellow sons. These inbred gave in F_2

two classes of females, namely, yellow and gray, and four classes of males,

namely, yellow and sable (non-cross-overs), wild type and the double

recessive yellow sable (cross-overs). From off-spring (F_3) of the F_2

yellow sable males by F_2 yellow females, pure stock of the double

recessive yellow sable was made up and used in the crosses to test linkage.

In color the yellow sable is quite similar to yellow black, that is, a rich

brown with a very dark brown trident pattern on the thorax. Yellow sable is

easier to distinguish from yellow than is yellow black, even when the flies

have not yet acquired their adult body-color.

Yellow sable males were bred to wild females and F_1 consisted of wild-type

males and females. These inbred gave the results shown in table 8. {36}

TABLE 8.--_P_1 wild [female] [female] x yellow sable [male] [male]. F_1

wild-type [female] [female] x F_1 wild-type [male] [male]._

+-----------+---------+--------------+--------------+-------+-----------+

| Reference.| type +-------+------+-------+------+ Total |Cross-over |

+-----------+---------+-------+------+-------+------+-------+-----------+

| | | | | | | | |

| 44 I | 292 | 110 | 43 | 75 | 36 | 264 | 42 |

| 45 I | 384 | 104 | 58 | 71 | 60 | 293 | 45 |

| +---------+--------------+-------+------+-------+-----------+

| Total | 676 | 214 | 101 | 146 | 96 | 557 | 43 |

| | | | | | | | |

+-----------+---------+-------+------+-------+------+-------+-----------+

Some of the F_1 females were back-crossed to yellow sable males and gave

the data for table 9.

TABLE 9.--_P_1 wild-type [female] [female] x yellow sable [male] [male]. B.

C. F_1 wild-type [female] x yellow sable [male] [male]._

+----------+-------------------------+---------------+-------+----------+

| | | | | |

| | | | | |

|Reference.+-----------+-------------+-------+-------+ Total.|Cross-over|

| | | | | | | |

+----------+-----------+-------------+-------+-------+-------+----------+

| | | | | | | |

| 31 I | 108 | 51 | 58 | 56 | 273 | 42 |

| 49 I | 265 | 175 | 161 | 169 | 770 | 43 |

| +-----------+-------------+-------+-------+-------+----------+

| Total | 373 | 226 | 219 | 225 | 1,043 | 43 |

| | | | | | | |

+----------+-----------+-------------+-------+-------+-------+----------+

In these tables the last column (to the right) shows for each culture the

amount of crossing-over between yellow and sable. These values are found by

dividing the number of cross-overs by the total number of individuals which

might show crossing-over, that is, males only or both males and females, as

the case may be. Free assortment would give 50 per cent of cross-overs and

absolute linkage 0 per cent of cross-overs. Except where the percentage of

crossing-over is very small these values are expressed to the nearest unit,

since the experimental error might make a closer calculation misleading.

The combined data of tables 8 and 9 give 686 cross-overs in a total of

1,600 individuals in which crossing-over might occur. The females of table

8 are all of one class (wild type) and are useless for this calculation

except as a check upon viability. The cross-over value of 43 per cent shows

that crossing-over is very free. We interpret this to mean that sable is

far from yellow in the chromosome. Since yellow is at one end of the known

series, sable would then occupy a locus somewhere near the opposite end.

This can be checked up by finding its linkage relations to the other

sex-linked factors. {37}

LINKAGE OF CHERRY AND SABLE.

The origin of cherry eye-color (Plate II, fig. 9) has been given by Safir

(Biol. Bull., 1913). From considerations which will be discussed later in

this paper we regard cherry as allelomorphic to white in a quadruple

allelomorph system composed of white, eosin, cherry, and their normal red

allelomorph. Cherry will then occupy the same locus as white, which is one

unit to the right of yellow, and will show the same linkage relations to

other factors as does white. A slightly lower cross-over value should be

given by cherry and sable than was given by yellow and sable.

When cherry (gray) females were crossed to (red) sable males the daughters

were wild type and the sons cherry. Inbred these gave the results shown in

table 10.

TABLE 10.--_P_1 cherry [female][female] x sable [male][male]. F_1 wild-type

[female] x F_1 cherry [male] [male]._

+---------+---------+---------+--------------+------------+------+------+

+---------+---------+---------+-------+------+------+-----+------+------+

| | | | | | | | | |

| 24 I | 94 | 105 | 51 | 42 | 20 | 43 | 156 | 40 |

| 55 I | 101 | 131 | 63 | 52 | 38 | 48 | 201 | 43 |

| 55' I | 96 | 94 | 52 | 31 | 29 | 30 | 142 | 42 |

| +---------+---------+-------+------+------+-----+------+------+

| Total | 291 | 330 | 166 | 125 | 87 | 121 | 499 | 42 |

| | | | | | | | | |

+---------+---------+---------+-------+------+------+-----+------+------+

The percentage of crossing-over between cherry and sable is 42. Since

cherry is one point from yellow, this result agrees extremely well with the

value 43 for yellow and sable. Since yellow and eosin lie at the left end

of the first chromosome, the high values, namely, 43 and 42, agree in

making it very probable that sable lies near the other end (_i. e._, to the

right). Sable will lie farther to the right than vermilion, for vermilion

has been shown elsewhere to give 33 per cent of crossing-over with eosin.

The location of sable to the right of vermilion has in fact been

substantiated by all later work.

LINKAGE OF EOSIN, VERMILION, AND SABLE.

Three loci are involved in the next experiment. Since eosin is an

allelomorph of cherry, it should be expected to give with sable the same

cross-over value as did cherry. When eosin (red) sable females were crossed

to (red) vermilion (gray) males, the daughters were wild type and the males

were eosin sable. Inbred these gave the classes shown in table 11. {38}

TABLE 11.--_P_1 eosin sable [female] x vermilion [male][male]. F_1

wild-type [female][female] x F_1 eosin sable [male][male]._

+------+--------------------------+

| | |

| | F_2 females. |

| | |

| +------------+-------------+

| | w^e s | w^e |

|Refer-| ---------- | -----+----- |

| | | s |

|ence. +------+-----+------+------+

| | | | | |

| | | | | |

+------+------+-----+------+------+

| | | | | |

| 26 I | 132 | 171 | 113 | 109 |

| 26'I | 96 | 146 | 86 | 78 |

| +------+-----+------+------+

|Total.| 228 | 317 | 199 | 187 |

+------+------+-----+------+------+

+------+---------------------------------------------------------+

| | |

| | F_2 males. |

| | |

| +---------------+--------------+-------------+------------+

| | w^e s | w^e v | w^e | w^e v s |

|Refer-| ----------- | -----+----- | --------+-- | ---+---+-- |

| | v | s | v s | |

|ence. +-------+-------+-------+------+------+------+------+-----+

| | | | | | | | | |

~ | Eosin |Ver- |ver- |Sable.|Eosin.|milion|ver- |Wild-|

+------+-------+-------+-------+------+------+------+------+-----+

| | | | | | | | | |

| 26 I | 127 | 163 | 75 | 76 | 37 | 14 | 2 | 5 |

| 26'I | 74 | 128 | 76 | 59 | 18 | 21 | 4 | 3 |

| +-------+-------+-------+------+------+------+------+-----+

|Total.| 201 | 291 | 151 | 135 | 55 | 35 | 6 | 8 |

+------+-------+-------+-------+------+------+------+------+-----+

If we consider the male classes of table 11, we find that the smallest

classes are eosin vermilion sable and wild type, which are the expected

double cross-over classes if sable lies to the right of vermilion, as

indicated by the crosses with eosin and with yellow. The classes which

represent single crossing-over between eosin and vermilion are eosin

vermilion, and sable, and those which represent single crossing-over

between vermilion and sable are eosin and vermilion sable. These relations

are seen in diagram II.

w^e V s

--+--------------------------------------------------+--------------+

X X

--+--------------------------------------------------+--------------+

W v S

DIAGRAM II.--The upper line represents an X chromosome, the lower line its

mate. The cross connecting lines indicate crossing-over between pairs of

factors.

w^e s {Eosin sable.

Non-cross-overs -------------------------- {

v {Vermilion.

w^e v {Eosin vermilion.

Single cross-overs ------------+------------- {

s {Sable.

w {Eosin.

-----------------------+-- {

v s {Vermilion sable.

w^e v s {Eosin vermilion sable.

Double cross-overs ------------+----------+-- {

{Wild-type.

If we consider the female classes of table 11, we get information as to the

cross-over value of eosin and sable, namely, 42 units. The male classes

will be considered in connection with the cross that follows.

The next experiment involves the same three gens which now enter in

different relations. A double recessive, eosin vermilion (gray) female {39}

was mated to (red red) sable males and gave 202 wild-type[5] females and

184 eosin vermilion males. Two F_1 pairs gave the results shown in table 12

(the four classes of females not being separated).

TABLE 12.--_P_1 eosin vermilion F_1 wild-type [female] x F_1 eosin

vermilion [male] [male]._

+------+--------+-------------------------------------------------------+

| | | F_2 males. |

| | +-------------+-------------+-------------+-------------+

| | | w^e v | w^e s | w^e v s | w^e |

| | | ----------- | -----+----- | --------+-- | ----+---+-- |

|Refer-| F_2 | s | v | | v s |

| ence.|females.+------+------+------+------+------+------+------+------+

+------+--------+------+------+------+------+------+------+------+------+

| 59 C | 133 | 40 | 33 | 7 | 16 | 5 | 5 | 2 | 1 |

| 61 C | 101 | 34 | 26 | 8 | 11 | 3 | 7 | 1 | 0 |

| +--------+------+------+------+------+------+------+------+------+

|Total | 234 | 74 | 59 | 15 | 27 | 8 | 12 | 3 | 1 |

+------+--------+------+------+------+------+------+------+------+------+

If we combine the data for males given in table 12 with those of table 11,

we get the following cross-over values. Eosin vermilion, 32; vermilion

sable, 12; eosin sable, 41.

{40}

LINKAGE OF MINIATURE AND SABLE.

The miniature wing has been described (Morgan, Science, 1911) and the wing

figured (Morgan, Jour. Exp. Zool., 1911). The gen for miniature lies about

3 units to the right of vermilion, so that it is still closer to sable than

is vermilion. The double recessive, miniature sable, was made up, and males

of this stock were bred to wild females (long gray). The wild-type

daughters were back-crossed to double recessive males and gave the results

(mass cultures) shown in table 13.

TABLE 13.--_P_1 wild [female] [female] x miniature sable [male] [male]. B.

C. F_1 wild-type [female] [female] x miniature sable [male] [male]._

+-----------+---------------------+-----------------+-------+-------+

| | | | | |

| Reference.+----------+----------+----------+------+ Total.| over |

+-----------+----------+----------+----------+------+-------+-------+

| | | | | | | |

| 38 I | 245 | 283 | 15 | 17 | 560 | 6 |

| 43 I | 191 | 236 | 13 | 18 | 458 | 7 |

| 46 I | 232 | 274 | 24 | 21 | 551 | 8 |

| +----------+----------+----------+------+-------+-------+

| Total | 668 | 793 | 52 | 56 | 1,569 | 7 |

| | | | | | | |

+-----------+----------+----------+----------+------+-------+-------+

Since the results for the male and the female classes are expected to be

the same, the sexes were not separated. The combined data give 7 per cent

of crossing-over between miniature and sable.

LINKAGE OF VERMILION, SABLE, AND BAR.

Bar eye has been described by Mrs. S. C. Tice (1914). It is a dominant

sex-linked character, whose locus, lying beyond vermilion and sable, is

near the right end of the chromosome series, that is, at the end opposite

yellow.

In the first cross of a balanced series of experiments for the gens

vermilion, sable, and bar, vermilion (gray not-bar) entered from one side

([female]) and (red) sable bar from the other ([male]). The daughters were

bar and the sons vermilion. The daughters were back-crossed singly to the

triple recessive males vermilion sable (not-bar), and gave the data

included in table 14.

In the second cross, vermilion sable (not-bar) went in from one side

([female]) and (red, gray) bar from the other. The daughters were bar and

the sons were vermilion sable. Since these sons have the three recessive

factors, inbreeding of F_1 is equivalent to a triple back-cross. The

results are given by pairs in table 15. {41}

TABLE 14.--_P_1 vermilion [female] [female] x sable bar [male] [male]. B.

C. F_1 bar [female] x vermilion sable [male] [male]._

+------+------------+-----------+------------+-----------+

| | v | v s B' | v B' | v s |

| | ---------- | ---+----- | -----+---- | --+--+--- |

| | s B' | | s | B' |

| +------+-----+-----+-----+-----+------+------+----+

| | | | bar.| | bar.| |sable.| |

+------+------+-----+-----+-----+-----+------+------+----+

| | | | | | | | | |

|147 I | 81 | 66 | 12 | 15 | 15 | 18 | | ~

|148 I | 103 | 108 | 4 | 19 | 11 | 11 | | ~

|149 I | 97 | 88 | 10 | 8 | 17 | 17 | 1 | 1 |

|150 I | 95 | 75 | 10 | 11 | 21 | 22 | 1 | 1 |

|151 I | 116 | 96 | 11 | 15 | 23 | 26 | | 2 |

| 89 | 89 | 94 | 10 | 19 | 15 | 11 | 1 | |

| 90 | 49 | 50 | 4 | 8 | 15 | 14 | | |

| 91 | 104 | 88 | 13 | 15 | 12 | 12 | | |

| +------+-----+-----+-----+-----+------+------+----+

|Total.| 734 | 665 | 74 | 110 | 129 | 131 | 3 | 4 |

| | | | | | | | | |

+------+------+-----+-----+-----+-----+------+------+----+

+------+------+------------------+

| | | |

| | |Cross-over values.|

| | | |

| | +------+-----+-----+

| | |sable.| bar.|bar. |

+------+------+------+-----+-----+

| | | | | |

~147 I | 207 | 13 | 16 | 29 |

~148 I | 256 | 9 | 9 | 18 |

|149 I | 239 | 8 | 15 | 22 |

|150 I | 236 | 10 | 19 | 27 |

|151 I | 289 | 10 | 18 | 26 |

| 89 | 239 | 13 | 11 | 23 |

| 90 | 140 | 9 | 21 | 29 |

| 91 | 244 | 11 | 10 | 21 |

| +------+------+-----+-----+

|Total.|1,850 | 10 | 14 | 24 |

| | | | | |

+------+------+------+-----+-----+

TABLE 15.--_P_1 vermilion sable [female] [female] x bar [male] [male]. B.

C. F_1 bar [female] x vermilion sable [male] [male]._

+------+----------+------------+-----------+------------+

| | v s | v B' | v s B' | v |

| | -------- | ---+------ | -----+--- | --+---+--- |

| | B' | s | | s B' |

| +------+---+-----+------+-----+-----+------+-----+

| |sable.| | bar.| | bar.| | | |

+------+------+---+-----+------+-----+-----+------+-----+

|105 I | 41 | 75| 10 | 4 | 5 | 11 | | ~

|106 I | 59 |122| 16 | 13 | 11 | 17 | | ~

|107 I | 92 | 98| 8 | 12 | 16 | 10 | | |

|116 I | 111 |149| 19 | 16 | 20 | 19 | | 1 |

|117 I | 92 |117| 16 | 14 | 15 | 18 | | |

|126 I | 96 |160| 13 | 13 | 17 | 35 | | |

|127 I | 117 |124| 13 | 25 | 24 | 30 | 1 | |

| +------+---+-----+------+-----+-----+------+-----+

|Total | 608 |845| 95 | 97 | 108 | 140 | 1 | 1 |

+------+------+---+-----+------+-----+-----+------+-----+

+------+------+------------------+

| | | |

| | |Cross-over values.|

| | | |

| | +------+-----+-----+

| | |sable.| bar.|bar. |

+------+------+------+-----+-----+

~105 I | 146 | 10 | 11 | 21 |

~106 I | 238 | 12 | 12 | 24 |

|107 I | 236 | 9 | 11 | 20 |

|116 I | 335 | 11 | 12 | 22 |

|117 I | 272 | 11 | 12 | 23 |

|126 I | 334 | 8 | 15 | 23 |

|127 I | 334 | 12 | 16 | 28 |

| +------+------+-----+-----+

|Total |1,895 | 10 | 13 | 23 |

+------+------+------+-----+-----+

{42}

In the third cross, vermilion (gray) bar entered from one side ([female])

and (red) sable (not-bar) from the other ([male]). The daughters are bar

and the sons vermilion bar. The daughters were back-crossed singly to

vermilion sable males and gave the data in table 16.

TABLE 16.--_P_1 vermilion bar_ [female] [female] x _sable_ [male] [male].

_B. C. F_1 bar_ [female] x _vermilion sable_ [male] [male].

+-----------+--------------+------------+-------------+---------------+

| | v B' | v s | v | v s B' |

| | ----- | -+------ | -----+-- | -+---+-- |

|Reference. | s | B' | s B' | |

| +-------+------+------+-----+-------+-----+---------+-----+

| | Ver- |Sable.| Ver- | Bar.| Ver- |Sable|Vermilion|Wild-|

| | bar. | |sable.| | | | bar. | |

+-----------+-------+------+------+-----+-------+-----+---------+-----+

| 129 I | 132 | 147 | 15 | 15 | 19 | 21 | 1 | 1 ~

| 130 I | 194 | 168 | 21 | 17 | 28 | 25 | .. | 1 ~

| 131 I | 121 | 89 | 10 | 20 | 26 | 11 | 1 | 1 |

| 137 I | 139 | 113 | 19 | 12 | 33 | 14 | .. | 1 |

| 138 I | 131 | 128 | 11 | 11 | 28 | 24 | 1 | .. |

| 139 I | 83 | 79 | 4 | 12 | 17 | 12 | .. | .. |

| +-------+------+------+-----+-------+-----+---------+-----+

| Total. | 800 | 724 | 80 | 87 | 151 | 107 | 3 | 4 |

+-----------+-------+------+------+-----+-------+-----+---------+-----+

+-----------+-------+-------------------------+

| | | |

|Reference. | Total.| Cross-over values. |

| | +---------+-----+---------+

| | |sable. |bar. |bar. |

+-----------+-------+---------+-----+---------+

~ 129 I | 351 | 9 | 12 | 20 |

~ 130 I | 454 | 9 | 12 | 20 |

| 131 I | 279 | 12 | 14 | 24 |

| 137 I | 331 | 10 | 15 | 24 |

| 138 I | 334 | 7 | 16 | 22 |

| 139 I | 207 | 8 | 14 | 22 |

| +-------+---------+-----+---------+

| Total. | 1,956 | 9 | 14 | 22 |

+-----------+-------+---------+-----+---------+

In the fourth cross, vermilion sable bar entered from one side, and (red

gray not-bar) wild type from the other. The daughters were bar and the sons

vermilion sable bar. The daughters were back-crossed singly to vermilion

sable males, with the results shown in table 17.

TABLE 17.--_P_1 vermilion sable bar_ [female] [female] x _wild_ [male]

[male]. _B. C. F_1 bar_ [female] x _vermilion sable_ [male] [male].

+-----------+---------------+--------------+------------+--------------+

| | v s B' | v | v s | v B' |

| | -------- | -+----- | -----+-- | -+-+-- |

| Reference.| | s B' | B' | s |

| +---------+-----+--------+-----+-------+----+-------+------+

| |Vermilion|Wild-| Ver- |Sable| Ver- |Bar.| Ver- |Sable.|

| | bar. | | | | sable.| | bar. | |

+-----------+---------+-----+--------+-----+-------+----+-------+------+

| 132 I | 95 | 108 | 10 | 13 | 24 | 22 | .. | .. ~

| 133 I | 112 | 150 | 18 | 16 | 26 | 16 | 1 | 2 ~

| 134 I | 84 | 95 | 14 | 7 | 15 | 16 | .. | 1 |

| 135 I | 100 | 86 | 16 | 17 | 19 | 22 | .. | 1 |

| 152 I | 73 | 88 | 12 | 8 | 14 | 18 | .. | .. |

| 153 I | 114 | 138 | 12 | 12 | 17 | 17 | .. | .. |

| 154 I | 63 | 90 | 10 | 8 | 8 | 15 | .. | .. |

| | | | | | | | | |

| Total. | 641 | 755 | 92 | 81 | 123 |126 | 1 | 4 |

+-----------+---------+-----+--------+-----+-------+----+-------+------+

+-----------+------+-------------------------+

| | | |

| Reference.|Total.| Cross-over values. |

| | +---------+-----+---------+

| | |sable. |bar. |bar. |

+-----------+------+---------+-----+---------+

~ 132 I | 272 | 9 | 17 | 25 |

~ 133 I | 341 | 11 | 13 | 22 |

| 134 I | 232 | 10 | 14 | 22 |

| 135 I | 261 | 13 | 16 | 28 |

| 152 I | 213 | 9 | 15 | 24 |

| 153 I | 310 | 8 | 11 | 19 |

| 154 I | 194 | 9 | 12 | 21 |

| | | | | |

| Total. |1,823 | 10 | 14 | 23 |

+-----------+------+---------+-----+---------+

{43}

In tables 14 to 17 the calculations for the three cross-over values for

vermilion, sable, and bar are given for the separate cultures and for the

totals. The latter are here repeated.

+-----------+-----------+---------+-----------+

| | sable. | bar. | bar. |

+-----------+-----------+---------+-----------+

| Table 14 | 10 | 14 | 24 |

| 15 | 10 | 13 | 23 |

| 16 | 9 | 14 | 22 |

| 17 | 10 | 14 | 23 |

+-----------+-----------+---------+-----------+

The results of the different experiments are remarkably uniform. There can

be no doubt that the cross-over value is independent of the way in which

the experiment is made, whether any two recessives enter from the same or

from opposite sides.

TABLE 18.--_Linkage of vermilion, sable, and bar with balanced viability._

+---------------------+---------+---------+---------+---------+-------+

| | ------- | --+---- | ----+-- | --+-+-- | Total.|

+---------------------+---------+---------+---------+---------+-------+

| Wild-type | 755 | 110 | 140 | 4 | |

| Vermilion | 734 | 92 | 151 | 1 | |

| Sable | 724 | 97 | 131 | 4 | |

| Bar | 845 | 87 | 126 | 4 | |

| Vermilion sable | 608 | 80 | 123 | 3 | |

| Vermilion bar | 800 | 95 | 129 | 1 | |

| Sable bar | 665 | 81 | 107 | 1 | |

| Vermilion sable bar | 641 | 74 | 108 | 3 | |

| +---------+---------+---------+---------+-------+

| Total | 5,772 | 716 | 1,015 | 21 | 7,524 |

| Percentage | 76.7 | 9.53 | 13.49 | 0.28 | |

+---------------------+---------+---------+---------+---------+-------+

In table 18 the data from each of the four separate experiments have been

combined in the manner explained, so that viability is canceled to the

greatest extent. The amount of each kind of cross-over appears at the

bottom of the table. The total amount of crossing-over between vermilion

and sable is the sum of the single (9.53) and of the double (0.28)

cross-overs, which value is 9.8. Likewise the cross-over value for sable

bar is 13.49 + 0.28 (= 14), and for vermilion bar is 9.53 + 13.49 (= 23).

By means of these cross-over values we may calculate the coincidence

involved, which is in this case

0.0028 x 100

--------------------------------- = 20.8

0.0953 + 0.0028 x 0.1349 + 0.0028

This value shows that there actually occurs only about 21 per cent of the

double cross-overs which from the values of the single cross-overs are

expected to occur in this section of the chromosome. This is the result

which is to be anticipated upon the chromosome view, for if crossing-over

is connected with loops of the chromosomes, and if these loops have an

average length, then if the chromosomes cross over at one {44} point it is

unlikely they will cross over again at another point nearer than the

average length of the loop.

The calculation of the locus for sable gives 43.0.

DOT.

In the F_2, from a cross of a double recessive (white vermilion) female by

a triple recessive (eosin vermilion pink) male, there appeared, July 21,

1912, three white-eyed females which had two small, symmetrically placed,

black, granular masses upon the thorax. These "dots" appeared to be dried

exudations from pores. It did not seem possible that such an effect could

be inherited, but as this condition had never been observed before, it

seemed worth while to mate the three females to their brothers. In the next

generation about 1 per cent of the males were dotted. From these females

and males a stock was made up which in subsequent generations showed from

10 to 50 per cent of dot. Selection seemed to have no effect upon the

percentage of dot. Although the stock never showed more than 50 per cent of

dot, yet it was found that the normal individuals from the stock threw

about the same per cent as did those that were dotted, so that the stock

was probably genetically pure. The number of males which showed the

character was always much smaller than the number of dotted females; in the

hatches which produced nearly 50 per cent of dot, nearly all the females

but very few of the males were dotted. Quite often the character showed on

only one side of the thorax.

Since this character arose in an experiment involving several eye-colors an

effort was made by crossing to wild and extracting to transfer the dot to

flies normal in all other respects. This effort succeeded only partly, for

a stock was obtained which differed from the wild type only in that it bore

dot (about 30 per cent) and in that the eyes were vermilion. Several

attempts to get the dot separated from vermilion failed. Since this was

only part of the preliminary routine work necessary to get a mutant stock

in shape for exact experimentation, no extensive records were kept.

LINKAGE OF VERMILION AND DOT.

When a dot male with vermilion eyes was bred to a wild female the offspring

were wild-type males and females. These inbred gave the data shown in table

19.

TABLE 19.--_P_1 vermilion dot [male] x wild [female] [female]. F_1

wild-type [female] [female] x F_1 wild-type [male] [male]._

+------------+----------+-----------+-----------+-------------+---------+

+------------+----------+-----------+-----------+-------------+---------+

| 7 | 345 | 151 | 130 | 0 | 0 |

| 8 | 524 | 245 | 220 | 3 | 0 |

| +----------+-----------+-----------+-------------+---------+

| Total. | 869 | 396 | 350 | 3 | 0 |

+------------+----------+-----------+-----------+-------------+---------+

{45}

Only three dot individuals appeared in F_2, but since these were males the

result indicates that the dot character is due to a sex-linked gen. These

three males had also vermilion eyes, indicating linkage of dot and

vermilion. The males show no deficiency in numbers, therefore the

non-appearance of the dot can not be due to its being semi-lethal. It

appears, therefore, that the expression of the character must depend on the

presence of an intensifying factor in one of the autosomes, or more

probably, like club, it appears only in a small percentage of flies that

are genetically pure for the character.

The reciprocal cross (dot female with vermilion eyes by wild male) was made

(table 20). The daughters were wild type and the sons vermilion. Not one of

the 272 sons showed dot. If the gen is sex-linked the non-appearance of dot

in the F_1 males can be explained on the ground that males that are

genetically dot show dot very rarely, or that its appearance is dependent

upon the intensification by an autosomal factor of the effect produced by

the sex-linked factor for dot.

TABLE 20.--_P_1 vermilion dot [female] x wild [male]._

A = Wild-type [female].

B = Vermilion [male].

C = Wild-type [male].

D = Wild-type [female].

E = Vermilion [male].

F = Vermilion [female].

G = Vermilion dot [male].

H = Vermilion dot [female].

I = Dot [male].

J = Dot [female].

+--------------------++-----------------------------------------------+

| First generation. || Second generation. |

+----------+----+----++----------+----+----+----+----+----+---+---+---+

|Reference.| A | B ||Reference.| C | D | E | F | G | H | I | J |

+--------------------++----------+----+----+----+----+----+---+---+---+

| 137 C. | 44 | 45 || 19 |211 |198 |228 |206 | 20 | 3 | 0 | 0 |

| 138 C. | 77 | 62 || 22 |266 |220 |227 |227 | 16 | 0 | 0 | 0 |

| |124 |124 || 28 |143 |149 |125 |124 | 14 | 1 | 0 | 0 |

| | 57 | 41 || +----+----+----+----+----+---+---+---+

| |----|----|| Total.|620 |567 |570 |557 | 50 | 4 | 0 | 0 |

| Total.|291 |272 || | | | | | | | | |

+--------------------++----------+----+----+----+----+----+---+---+---+

The F_2 generation is given in table 20. The dot reappeared in F_2 both in

females and in males, but instead of appearing in 50 per cent of both

sexes, as expected if it is simply sex-linked, it appeared in 4.0 per cent

in the females and in only 0.4 per cent in the males. The failure of the

character to be fully realized is again apparent, but here, where it is

possible for it to be realized equally in males and females, we find that

there are 50 females with dot to only 4 dot males. This would indicate that

the character is partially "_sex-limited_" (Morgan, 1914_d_) in its

realization. The dot appeared only in flies with vermilion eyes, indicating

extremely strong linkage between vermilion and dot.

The evidence from the history of the stock, together with these

experiments, shows that the character resembles club (wing) in that it is

not expressed somatically in all the flies which are homozygous for it. In

the case of club we were fortunate enough to find a constant feature {46}

which we could use as an index, but, so far as we have been able to see,

there is no such constant accessory character in the case of the dot.

Unlike club, dot is markedly sex-limited in its effect; that is, there is a

difference of expression of the gen in the male and female. This difference

recalls the sexual dimorphism of the eosin eye.

BOW.

In an F_2 generation from rudimentary males by wild females there appeared,

August 15, 1912, a single male whose wings instead of being flat were

turned down over the abdomen (fig. c). The curvature was uniform throughout

the length of the wing. A previous mutation, arc, of this same type had

been found to be a recessive character in the second group. The new

mutation, bow, is less extreme than arc and is more variable in the amount

of curvature. When the bow male was mated to wild females the offspring had

straight wings.

[Illustration: FIG. C.--Bow wing.]

TABLE 21.--_P_1 bow [male][male] x wild [female][female]._

+------------------------------------------+

| First generation. |

+----------+-----------------+-------------+

|Reference.| Wild-type | Wild-type ~

| |[female][female].|[male][male].~

+----------+-----------------+-------------+

| 169 C. | 17 | 17 |

+----------+-----------------+-------------+

+--------------------------------------------------------+

| Second generation. |

+----------+-----------------+-------------+-------------+

~Reference.| Wild-type | Wild-type | Bow |

~ |[female][female].|[male][male].|[male][male].|

+----------+-----------------+-------------+-------------+

| 18 I. | 193 | 145 | 67 |

| 21 I | 182 | 100 | 49 |

| +-----------------+-------------+-------------+

| Total.| 375 | 245 | 116 |

+----------+-----------------+-------------+-------------+

{47}

The F_2 ratio in table 21 is evidently the 2:1:1 ratio typical of

sex-linkage, but with the bow males running behind expectation. This

deficiency is due in part to viability but more to a failure to recognize

all the bow-winged individuals, so that some of them were classified among

the not-bow or straight wings. In favor of the view that the classification

was not strict is the fact that the sum of the two male classes about

equals the number of the females.

BOW BY ARC.

When this mutant first appeared its similarity to arc led us to suspect

that it might be arc itself or an allelomorph of arc. It was bred,

therefore, to arc. The bow male by arc females gave straight (normal)

winged males and females. The appearance of straight wings shows that bow

is not arc nor allelomorphic to arc. When made later, the reciprocal cross

of bow female by arc male gave in F_1 straight-winged females but bow

males. This result is in accordance with the interpretation that bow is a

sex-linked recessive. Further details of these last two experiments may now

be given. The F_1 (wild-type) flies from bow male by arc female were

inbred. The data are given in table 22.

TABLE 22.--_P_1 bow [male] x arc [female]._

+--------------------------------------------+

| First generation. |

+----------+------------------+--------------+

|Reference.| Wild-type | Wild-type ~

| |[female] [female].|[male] [male].~

+----------+------------------+--------------+

| 71 C. | 48 | 43 |

| 75 C. | 28 | 27 |

| +------------------+--------------+

| Total.| 76 | 70 |

+----------+------------------+--------------+

+------------------------------+

| Second generation. |

+----------+---------+---------+

~Reference.|Straight.| Not- |

~ | |straight.|

+----------+---------+---------+

| 71 C. | 179 | 133 |

+----------+---------+---------+

Bow and arc are so much alike that they give a single rather variable

phenotypic class in F_2. Therefore the F_2 generation is made up of only

two separable classes--flies with straight wings and flies with

not-straight wings. The ratio of the two should be theoretically 9:7, which

is approximately realized in 179:133.

If the distribution of the characters according to sex is ignored, the case

is similar to the case of the two white races of sweet peas, which bred

together gave wild-type or purple peas in F_1 and in F_2 gave 9 colored to

7 white. If sex is taken into account, the theoretical expectation for the

F_2 females is 6 straight to 2 arc, and for the F_2 males 3 straight to 1

arc to 3 bow to 1 bow-arc.

The F_1 from bow females by arc male and their F_2 offspring are given in

table 23. {48}

TABLE 23.--_P_1 bow [female] x arc [male]._

+--------------------------------------------+

| First generation. |

|----------+------------------+--------------+

|Reference.| Wild-type | Bow |

| |[female] [female].|[male] [male].|

|----------+------------------+--------------+

| 72 C. | 22 | 19 ~

| 73 C. | 12 | 10 ~

| 5 I. | 22 | 21 |

| 74 C. | 56 | 52 |

| |------------------+--------------+

| Total.| 112 | 102 |

+----------+------------------+--------------+

+------------------------------+

| Second generation. |

+----------+---------+---------+

|Reference.|Straight.| Not- |

| | |straight.|

+----------+---------+---------+

~ 3 I. | 56 | 69 |

~ 3.1 I. | 46 | 62 |

| 5 I. | 56 | 68 |

| 5.1 I. | 90 | 108 |

+----------+---------+---------+

| Total.| 248 | 307 |

+----------+---------+---------+

In this case the F_2 expectation is 6 straight to 10 not-straight. Since

the sex-linked gen bow entered from the female, half the F_2 males and

females are bow. The half that are not-bow consist of 3 straight to 1 arc,

so that both in the female classes and in the male classes there are 3

straight to 5 not-straight or in all 6 straight to 10 not-straight. The

realized result, 248 straight to 307 not-straight, is more nearly a 3:4

ratio, due probably to a wrong classification of some of the bow as

straight.

LEMON BODY-COLOR.

(Plate I, figure 3.)

A few males of a new mutant with a lemon-colored body and wings appeared in

August 1912. The lemon flies (Plate II, fig. 3) resemble quite closely the

yellow flies (Plate II, fig. 4). They are paler and the bristles, instead

of being brown, are black. These flies are so weak that despite most

careful attention they get stuck to the food, so that they die before

mating. The stock was at first maintained in mass from those cultures that

gave the greatest percentage of lemon flies. In a few cases lemon males

mated with their gray sisters left offspring, but the stock obtained in

this way had still to be maintained by breeding heterozygotes, as stated

above. But from the gray sisters heterozygous for lemon (bred to lemon

males) some lemon females were also produced.

LINKAGE OF CHERRY, LEMON, AND VERMILION.

In order to study the linkage of lemon, the following experiment was

carried out. Since it was impracticable to breed directly from the lemon

flies, virgin females were taken from stock throwing lemon, and were mated

singly to cherry vermilion males. Only a few of the females showed

themselves heterozygous for lemon by producing lemon as well as gray sons.

Half the daughters of such a pair are expected to be heterozygous for lemon

and also for cherry and vermilion, which went in from the father. These

daughters were mated singly to cherry vermilion males, and those that gave

some lemon sons were continued, {49} and are recorded in table 24. The four

classes of females were not separated from each other, but the total of

females is given in the table.

TABLE 24.--_P_1 lemon (het.) [female] x cherry vermilion [male] [male]. F_1

wild-type [female] x cherry vermilion [male] [male]._

+-------+--------------+-------------+-------------+-------------+------+

| | W^c V | W^c l_m | W^c | W^c l_m V | |

| | ---------- | ---+------ | ------+--- | ---+----+---| |

| | l_m | V | l_m V | | |

|Females+-------+------+------+------+------+------+-------+-----+ Total|

+-------+-------+------+------+------+------+------+-------+-----+------+

| 71 | 42 | 19 | 2 | 6 | 3 | 6 | 0 | 0 | 78 |

| 88 | 26 | 19 | 2 | 8 | 8 | 4 | 0 | 0 | 67 |

| 36 | 28 | 7 | 0 | 2 | 1 | 0 | 0 | 0 | 38 |

| 51 | 12 | 22 | 0 | 4 | 4 | 4 | 0 | 0 | 46 |

| 98 | 29 | 35 | 0 | 8 | 5 | 1 | 0 | 0 | 78 |

| 47 | 17 | 11 | 0 | 1 | 3 | 2 | 0 | 0 | 34 |

| 46 | 23 | 20 | 1 | 6 | 5 | 2 | 0 | 0 | 57 |

+-------+-------+------+------+------+------+------+-------+-----+------+

| 437 | 177 | 133 | 5 | 35 | 29 | 19 | 0 | 0 | 398 |

+-------+-------+------+------+------+------+------+-------+-----+------+

There are three loci involved in this cross, namely, cherry, lemon, and

vermilion. Of these loci two were known, cherry and vermilion. The data are

consistent with the assumption that the lemon locus is between cherry and

vermilion, for the double cross-over classes (the smallest classes) are

cherry lemon vermilion and wild type. The number of single cross-overs

between cherry and lemon and between lemon and vermilion are also

consistent with this assumption. Since lemon flies fail to emerge

successfully, depending in part upon the condition of the bottle, the

classes involving lemon are worthless in calculating crossing-over and are

here ignored. In other words, lemon may be treated as though it did not

appear at all, _i. e._, as a lethal. The not-lemon classes--cherry,

vermilion, cherry vermilion, and wild type--give the following approximate

cross-over values for the three loci involved: Cherry lemon, 15; lemon

vermilion, 12; cherry vermilion, 27. The locus of lemon, calculated by

interpolation, is at about 17.5.

LETHAL 2.

In September 1912 a certain wild female produced 78 daughters and only 16

sons (Morgan, 1914_b_); 63 of these daughters were tested and 31 of them

gave 2 females to 1 male, while 32 of them gave 1:1 sex-ratios. This shows

that the mother of the original high sex-ratio was heterozygous for a

recessive sex-linked lethal. In order to determine the position of this

lethal, a lethal-bearing female was bred to an eosin (or white) miniature

male, and those daughters that were heterozygous for eosin, lethal, and

miniature were then back-crossed to {50} eosin miniature males. The

daughters that result from such a cross give only the amount of

crossing-over between eosin and miniature (as 29.7), but the males give the

cross-over values for eosin lethal (9.9), lethal miniature (15.4), and

eosin miniature (25.1). The data for this cross are given in table 25.

TABLE 25.--_Total data upon linkage of eosin, lethal 2, and miniature, from

Morgan, 1914b._

+------------------------------------+

| Females. |

+--------+--------------+------------+

| | | |

| Total. | Cross-overs. | Cross-over |

| | | value. ~

| | | ~

+--------+--------------+------------+

| 15,904 | 4,736 | 29.7 |

+--------+--------------+------------+

+-----------------------------------------------------------------------+

| Males. |

+--------+--------+--------+---------+----------------------------------+

|w^e m|w^e l_2 |w^e |w^e l_2 m| Cross-over values. |

|--------|---+----|------+-|---+---+-+----------+-----------+-----------+

~ l_2 | m| l_2 m| | Eosin | Lethal 2 | Eosin |

+--------+--------+--------+---------+----------+-----------+-----------+

| 5,045 | 653 | 1,040 | 14 | 9.9 | 15.4 | 25.1 |

+--------+--------+--------+---------+----------+-----------+-----------+

A similar experiment, in which eosin and vermilion were used instead of

eosin and miniature, is summarized in table 26.

TABLE 26.--_Total data upon the linkage of eosin, lethal 2, and vermilion,

from Morgan, 1914b._

+------------------------------------+

| Females. |

+--------+--------------+------------+

| | | |

| Total. | Cross-overs. | Cross-over |

| | | value. ~

| | | ~

+--------+--------------+------------+

| 2,656 | 729 | 27.5 |

+--------+--------------+------------+

+-----------------------------------------------------------------------+

| Males. |

+--------+--------+--------+---------+----------------------------------+

|w^e v|w^e l_2 |w^e |w^e l_2 v| Cross-over values. |

|--------|---+----|------+-|---+---+-+----------+-----------+-----------+

~ l_2 | v| l_2 v| | Eosin | Lethal 2 | Eosin |

+--------+--------+--------+---------+----------+-----------+-----------+

| 902 | 124 | 227 | 6 | 10.3 | 18.5 | 27.9 |

+--------+--------+--------+---------+----------+-----------+-----------+

Considerable data in which lethal was not involved were also obtained in

the course of these experiments and are included in the summary of the

total data given in table 27.

TABLE 27.--_Summary of all data upon lethal 2, from Morgan, 1914b._

+--------------------+--------+--------------+------------+

+--------------------+--------+--------------+------------+

| White lethal 2 | 8,011 | 767 | 9.6 |

| White vermilion | 6,023 | 1,612 | 26.8 |

| White miniature | 36,021 | 11,048 | 30.7 |

| Lethal 2 vermilion | 1,400 | 248 | 17.7 |

| Lethal 2 miniature | 6,752 | 1,054 | 15.4 |

+--------------------+--------+--------------+------------+

The amount of crossing-over between eosin and lethal is about 10 per cent

and the amount of crossing-over between lethal and miniature is about 18

per cent. Since the amount of crossing-over between eosin {51} and

miniature is over 30 per cent, the lethal factor must lie between eosin and

miniature, somewhat nearer to eosin. It is impossible at present to locate

lethal 2 accurately because of a real discrepancy in the data, which makes

it appear that lethal 2 extends for a distance of about 5 units along the

chromosome from about 10 to about 15. Work is being done which it is hoped

will make clear the reason for this. For the present we may locate lethal 2

at the midpoint of its range, or at 12.5.

CHERRY.

(Plate II, figure 9.)

The origin of the eye-color cherry has been given by Safir (Biol. Bull.,

1913).

Cherry appeared (October 1912) in an experiment involving vermilion

eye-color and miniature wings. This is the only time the mutant has ever

come up, and although several of this mutant (males) appeared in Safir's

experiment, they may have all come from the same mother. It is probable

that the mutation occurred in the vermilion stock only a generation or so

before the experiment was made, for otherwise cherry would be expected to

be found also in the vermilion stock from which the mothers were taken;

however, it was not found.

A SYSTEM OF QUADRUPLE ALLELOMORPHS.

Safir has described crosses between this eye-color and red, white, eosin,

and vermilion. We conclude for reasons similar to those given by Morgan and

Bridges (Jour. Exp. Zool., 1913) for the case of white and eosin, that

cherry is an allelomorph of white and of eosin. This is not the

interpretation followed in Safir's paper, where cherry is treated as though

absolutely linked to white or to eosin. Both interpretations give, however,

the same numerical result for each cross considered by itself. Safir's data

and those which appear in this paper show that white, eosin, cherry, and a

normal (red) allelomorph form a system of quadruple allelomorphs. If this

interpretation is correct, then the linkage relations of cherry should be

identical with those of white or of eosin.

LINKAGE OF CHERRY AND VERMILION.

The cross-over value for white (eosin) and vermilion, based on a very large

amount of data, is about 31 units. An experiment of our own in which cherry

was used with vermilion gave a cross-over value of 31 units, which is a

close approximation to the cross-over value of white and vermilion. The

cross which gave this data was that of a cherry vermilion (double

recessive) male by wild females. The F_{1} wild-type flies inbred gave a

single class of females (wild-type) and the males in four classes which

show by the deviation from a 1:1:1:1 ratio the amount of crossing-over

involved. {52}

In one of the F_{2} male classes of table 28 the simple eye-color cherry

appeared for the first time (since the original mutant was vermilion as

well as cherry). Safir has recorded a similar cross with like results.

TABLE 28.--_P_{1} cherry vermilion [male] [male] x wild [female] [female].

F_{1} wild-type [female] [female] x F_{1} wild-type [male] [male]._

+----------+---------+----------------+---------------+-------+------+

| |Wild-type+----------+-----+-------+-------+Total |Cross-|

+----------+---------+----------+-----+-------+-------+-------+------+

| 160 C | 188 | 57 | 61 | 32 | 34 | 184 | 36 |

| 161 C | 256 | 85 | 93 | 40 | 52 | 270 | 34 |

| 162 C | 251 | 78 | 78 | 20 | 37 | 213 | 26 |

| 163 C | 229 | 76 | 95 | 34 | 33 | 238 | 28 |

+----------+---------+----------+-----+-------+-------+-------+------+

| Total | 924 | 296 | 327 | 126 | 156 | 905 | 31 |

+----------+---------+----------+-----+-------+-------+-------+------+

Some cherry males were bred to wild females. The F_{1} wild-type males and

females inbred gave the results shown in table 29. Some of the cherry males

thus produced were bred to their sisters. Cherry females as well as males

resulted; and it was seen that the eye-color is the same in the males and

females, in contradistinction to the allelomorph eosin, where there is a

marked bicolorism (figs. 7, 8, Plate II). The cherry eye-color is almost

identical with that of the eosin female, but is perhaps slightly more

translucent and brighter.

TABLE 29.--_P_{1} cherry [male] [male] x wild [female] [female]. F_{1}

wild-type [female] [female] x F_{1} wild-type [male] [male]._

+------------+---------------------+-------------------+----------------+

+------------+---------------------+-------------------+----------------+

| 15 I | 266 | 120 | 100 |

+------------+---------------------+-------------------+----------------+

+------------+-------------------------------------+

| | First generation. |

| Reference. +--------------------+----------------+

| | White-cherry | |

| | compound [female]. | Cherry [male]. |

+------------+--------------------+----------------+

| 9 M | 321 | 302 |

+------------+--------------------+----------------+

Eosin-cherry compound was also made. An eosin female was mated to a cherry

male. The eosin-cherry daughters were darker than their eosin brothers.

Inbred they gave the results shown in table 31.

TABLE 31.--_P_1 eosin [female] x cherry [male]._

+------------------------------------------+

| First generation. |

+------------+-------------------+---------+

| | Eosin-cherry | Eosin |

| Reference. | compound | [male] |

| | [female][female]. | [male]. ~

| | | ~

+------------+-------------------+---------+

| 43C | 71 | 58 |

+------------+-------------------+---------+

+----------------------------------------------------+

| Second generation. |

+------------+-------------------+---------+---------+

~ | compound | [male]. | [male]. |

~ | [female][female]. | | |

+------------+-------------------+---------+---------+

| 1I | 154 | 99 | 62 |

| 2I | 174 | 74 | 77 |

| +-------------------+---------+---------+

| | 328 | 173 | 139 |

+------------+-------------------+---------+---------+

Although in the F_2 results there are two genotypic classes of females,

namely, pure eosin and eosin-cherry compound, the eye-colors are so nearly

the same that they can not be separated. The two classes of males can be

readily distinguished; of these, one class, cherry, has the same color as

the females, while the other class, eosin, is much lighter. Such an F_2

group will perpetuate itself, giving one type of female (of three possible

genotypic compositions, but somatically practically homogeneous) and two

types of males, only one of which is like the females.

FUSED.

In a cross between purple-eyed[6] males and black females there appeared in

F_2 (Nov. 4, 1912) a male having the veins of the wing arranged as shown in

text-figure D b. It will be seen that the third and the fourth longitudinal

veins are fused from the base to and beyond the {53} point at which in

normal flies the anterior cross-vein lies. The cross-vein and the cell

normally cut off by it are absent. There are a number of other features

(see fig. D _c_) characteristic of this mutation: the wings are held out at

a wide angle from the body, the ocelli are very much reduced in size or

entirely absent, the bristles around the ocelli are usually small. The

females are absolutely sterile, not only with their own, but with any

males.

Fused males by wild females gave wild-type males and females. Inbred these

gave the results shown in table 32. The fused character reappeared only in

the F_2 males, showing that it is a recessive sex-linked character.

TABLE 32.--_P_1 fused [male] x wild [female][female]._

+-------------------------------------------------+

| First generation. |

+------------+-------------------+----------------+

| Reference. | Wild-type | Wild-type ~

| | [female][female]. | [male][male]. ~

+------------+-------------------+----------------+

| 4I | 66 | 43 |

| | | |

+------------+-------------------+----------------+

+------------------------------------------------------------------+

| Second generation. |

+------------+-------------------+----------------+----------------+

~ Reference. | Wild-type | Wild-type | Fused |

~ | [female][female]. | [male][male]. | [male][male]. |

+------------+-------------------+----------------+----------------+

| 190C | 258 | 96 | 115 |

| 14I | 239 | 105 | 90 |

| +-------------------+----------------+----------------+

| Total | 497 | 201 | 205 |

+------------+-------------------+----------------+----------------+

The reciprocal cross was tried many times, but is impossible, owing to the

sterility of the females. Since the fused females are sterile to fused

males, the stock is kept up by breeding heterozygous females to fused

males.

By means of the following experiments the position of fused in the X

chromosome was determined. A preliminary test was made by mating with

eosin, whose factor lies near the left end of the X chromosome series.

LINKAGE OF EOSIN AND FUSED.

Fused (red-eyed) males mated to eosin (not-fused) females gave wild-type

daughters and eosin sons, which inbred gave the classes shown in table 33.

TABLE 33.--_P_1 eosin [female][female] x fused [male][male]. F_1 wild-type

[female][female] x F_1 eosin [male][male]._

+----------+--------+-----------------+----------------+-------+--------+

|Reference.|Females.+--------+--------+--------+-------+ males.| over |

+----------+--------+--------+--------+--------+-------+-------+--------+

| 56I | 496 | 131 | 113 | 82 | 104 | 430 | 43 |

+----------+--------+--------+--------+--------+-------+-------+--------+

{54}

The data give 43 per cent of crossing-over, which places fused far to the

right or to the left of eosin. The latter position is improbable, since

eosin already lies very near the extreme left end of the known series.

Therefore, since 43 per cent would place the factor nearly at the right end

of the series, the next step was to test its relation to a factor like bar

that lies at the right end of the chromosome. By mating to bar alone we

could only get the linkage to bar without discovering on which side of bar

the new factor lies, but by mating to a fly that carries still another

sex-linked factor, known to lie to the left of bar, the information gained

should show the relative order of the factors involved. Furthermore, since,

by making a back-cross, both males and females give the same kind of data

(and need not be separated), the experiment was made in this way. In order

to have material for such an experiment double mutant stocks of vermilion

fused and also of bar fused were made up.

[Illustration: Fig. D.--_a_, normal wing; _b_ and _c_, fused wings. _c_

shows a typical fused wing. The most striking feature is the closure of the

cell between the third and fourth longitudinal veins with the elimination

of the cross-vein; the veins at the base of the wing differ from those in

the normal shown in a. _b_ shows the normal position in which the fused

wings are held. The fusion of the veins in _b_ is unusually complete.]

{55}

LINKAGE OF VERMILION, BAR, AND FUSED.

Males from the stock of (red) bar fused were mated to vermilion (not-bar,

not-fused) females, and produced bar females and vermilion males. The bar

F_1 daughters were back-crossed to vermilion fused males and produced the

classes of offspring shown in table 34.

TABLE 34.--P_1 _vermilion_ [female] [female] x _bar fused_ [male] [male].

_B. C. F_1 bar_ [female] x _vermilion fused_ [male] [male].

+----------+-------------------+---------------------+------------------+

| | v | v B' f_u | v f_u |

| | ----------------- | ----+-------------- | -----------+---- |

| | B' f_u | | B' |

|Reference.+----------+--------+----------+----------+-----------+------+

| |Vermilion.| Bar | bar |Wild-type.| Vermilion | Bar. |

+----------+----------+--------+----------+----------+-----------+------+

|140 I | 137 | 130 | 35 | 40 | 5 | 8 ~

|141 I | 144 | 137 | 38 | 41 | 4 | 2 ~

|142 I | 153 | 120 | 43 | 58 | 6 | 7 |

|143 I | 153 | 92 | 44 | 41 | 3 | 7 |

|145 I | 69 | 62 | 29 | 19 | 1 | .. |

|146 I | 96 | 103 | 30 | 34 | 7 | 3 |

|156 I | 62 | 45 | 25 | 27 | 1 | 4 |

|157 I | 93 | 57 | 11 | 31 | 2 | 2 |

| +----------+--------+----------+----------+-----------+------+

| Total. | 907 | 746 | 255 | 291 | 29 | 33 |

+----------+----------+--------+----------+----------+-----------+------+

+--------------------+--------+--------------------------------+

| v B' | | |

| ----+--------+---- | | Cross-over values. |

| f_u | | |

+-----------+--------+ +-----------+--------+-----------+

| bar. | | | bar. | fused. | fused. |

+-----------+--------+--------+-----------+--------+-----------+

~ .. | .. | 355 | 21 | 4 | 25 |

~ .. | .. | 366 | 22 | 2 | 23 |

| 1 | .. | 388 | 26 | 4 | 29 |

| 3 | 1 | 344 | 26 | 4 | 28 |

| 1 | .. | 181 | 27 | 1 | 27 |

| .. | .. | 273 | 23 | 4 | 26 |

| .. | .. | 164 | 32 | 3 | 35 |

| .. | 2 | 198 | 22 | 3 | 23 |

+-----------+--------+--------+-----------+--------+-----------+

| 5 | 3 | 2,269 | 24 | 3 | 27 |

+-----------+--------+--------+-----------+--------+-----------+

The data show that the factor for fused lies about 3 units to the right of

bar. This is the furthest point yet obtained to the right. The reasons for

locating fused to the right of bar are that, if it occupies such a

position, then the double cross-over classes (which are expected to be the

smallest classes) should be vermilion bar and fused, and these are, in

fact, the smallest classes. The order of factors is, then, vermilion, bar,

fused. This order is confirmed by the result that the number of cross-overs

between fused and vermilion is greater than that between bar and vermilion.

In order to obtain data to balance viability effects, the following

experiment was made:

Vermilion (not-bar) fused males were bred to (red) bar (not-fused) females.

The daughters and sons were bar. The daughters were back-crossed, singly,

to vermilion fused males and gave the results shown in table 35. Each

female was also transferred to a second culture bottle, so that for each

female there are two broods given consecutively (82, 82', etc.) in table

35.

The results given by the two broods of the same female are similar. The

values are very near to those given in the last experiment, and confirm the

conclusions there drawn. The combined data give the results shown in table

36. {56}

TABLE 35.--_P_1 bar [female] [female] x vermilion fused [male] [male]. B.

C. F_1 bar [female] x vermilion fused [male] [male]._

A - Vermilion fused.

B - Bar.

C - Vermilion bar.

D - Fused.

E - Vermilion.

F - Bar fused.

G - Vermilion bar fused.

H - Wild type.

-------------------------------------------------------------------------

| v f_u | v B' |v |v B' f_u| | Cross-

| -------- |----+----|----+----|-+---+---| | over

| B' | f_u | B' f_u | |Total.| values.

Reference +-------------+---------+---------+---------+ +-----------

| A | B | C | D | E | F | G | H | | C | F | A

----------+------+------+----+----+----+----+----+----+------+---+---+---

| | | | | | | | | | | |

82 | 165 | 165 | 63 | 57 | 8 | 7 | 1 | .. | 466 | 26|3 | 29

82' | 104 | 87 | 26 | 24 | .. | 4 | .. | .. | 245 | 20|2 | 22

83 | 128 | 164 | 51 | 39 | 6 | 4 | .. | .. | 392 | 23|3 | 26

83' | 100 | 94 | 28 | 30 | 4 | 4 | .. | .. | 260 | 22|3 | 25

89 | 85 | 105 | 23 | 24 | 5 | 2 | .. | .. | 244 | 19|3 | 22

89' | 78 | 91 | 21 | 27 | 1 | 2 | .. | 1 | 221 | 22|2 | 23

90 | 86 | 85 | 30 | 28 | 5 | .. | .. | .. | 234 | 25|2 | 27

90' | 33 | 38 | 22 | 14 | 4 | 1 | .. | 1 | 113 | 33|5 | 36

91 | 125 | 107 | 41 | 31 | 1 | 1 | .. | .. | 306 | 24|1 | 24

91' | 91 | 95 | 31 | 25 | 5 | 1 | .. | 2 | 250 | 23|3 | 25

92 | 109 | 136 | 41 | 24 | 4 | 2 | .. | .. | 316 | 21|2 | 23

92' | 100 | 105 | 29 | 29 | .. | 1 | .. | 1 | 265 | 22|1 | 22

93 | 75 | 67 | 19 | 20 | .. | 1 | .. | .. | 182 | 21|1 | 22

93' | 68 | 94 | 31 | 17 | 1 | 1 | .. | .. | 212 | 23|1 | 24

94 | 84 | 96 | 31 | 35 | 8 | 1 | .. | .. | 255 | 26|4 | 29

94' | 61 | 73 | 20 | 22 | 5 | 4 | .. | .. | 185 | 23|5 | 28

95 | 84 | 102 | 27 | 26 | 3 | 3 | .. | .. | 245 | 22|2 | 24

96 | 144 | 148 | 43 | 34 | 1 | 2 | .. | 1 | 373 | 21|1 | 21

97 | 81 | 96 | 25 | 20 | 5 | 3 | .. | .. | 230 | 20|4 | 23

98 | 107 | 112 | 39 | 33 | 1 | 2 | .. | .. | 294 | 25|1 | 26

Firsts |1,273 |1,383 |433 |371 | 47 | 28 | 1 | 1 |3,537 | 23|2 | 25

Seconds | 635 | 677 |208 |188 | 20 | 18 | .. | 5 |1,751 | 23|3 | 25

----------+------+------+----+----+----+----+----+----+------+---+---+---

Total.|1,908 |2,060 |641 |559 | 67 | 46 | 1 | 6 |5,288 | 23|2.3| 25

----------+------+------+----+----+----+----+----+----+------+---+---+---

TABLE 36.--_Linkage of vermilion, bar, and fused with balanced viability._

+------------+----------+-----------+-----------+-----------+--------+

| | v B' f_u | v | v B' | v f_u | |

| | -------- | --+------ | -----+--- | -+---+--- | Total. |

| | | B' f_u | f_u | B' | |

+------------+----------+-----------+-----------+-----------+--------+

| | | | | | |

| | 5,621 | 1,756 | 175 | 15 | 7,567 |

| Percentage | 74.3 | 23.19 | 2.31 | 0.2 | |

| | | | | | |

+------------+----------+-----------+-----------+-----------+--------+

Some additional data bearing on the linkage of vermilion and fused were

obtained. Males of (red) fused stock were bred to vermilion (not-fused)

females, and gave wild-type females and vermilion males, which inbred gave

the results shown in table 37.

The percentage of cross-overs between vermilion and fused is here 27, which

is in agreement with the 26 per cent of the preceding experiment.

The converse experiment, namely, red (not-fused) females by vermilion fused

males also gave, when the wild-type daughters were {57} back-crossed to

vermilion fused males, a linkage value of 27 units. Two 10-day broods were

reared from each female. The data given in table 38 show that the

percentage of crossing-over does not change as the flies get older. The

locus of fused on the basis of all of the data is at 59.5.

TABLE 37.--P_1 vermilion [female] [female] x fused [male] [male]. F_1

wild-type [female] [female] x F_1 vermilion [male] [male].

KEY:

A: Non-cross-over [male] [male].

B: Cross-over [male] [male].

C: Females.

D: Vermilion.

E: Fused.

F: Vermilion fused.

G: Wild-type.

H: Total [male] [male].

I: Cross-over values.

+------------+-----+-----------+----------+-----+----+

| | | A | B | | |

| | +-----+-----+----+-----+ | |

| Reference. | C | D | E | F | G | H | I |

+------------+-----+-----+-----+----+-----+-----+----+

| 79 I | 299 | 93 | 96 | 37 | 36 | 262 | 28 |

| 80 I | 245 | 93 | 60 | 28 | 27 | 208 | 26 |

| 81 I | 263 | 101 | 63 | 22 | 40 | 226 | 27 |

| +-----+-----+-----+----+-----+-----+----+

| Total. | 807 | 287 | 219 | 87 | 103 | 696 | 27 |

+------------+-----+-----+-----+----+-----+-----+----+

TABLE 38.--P_1 wild [female] [female] x vermilion fused [male] [male]. F_1

wild-type [female] x F_1 wild-type [male] [male].

KEY:

A: Wild-type [female] [female].

B: Non-Cross-over [male].

C: Cross-over [male].

D: Vermilion fused.

E: Wild-type.

F: Vermilion.

G: Fused.

H: Total [male] [male].

I: Cross-over values.

+------------+-------+------------+-----------+-----+----+

| | | B | C | | |

| | +-----+------+-----+-----+ | |

| Reference. | A | D | E | F | G | H | I |

+------------+-------+-----+------+-----+-----+-----+----+

| 52 | 96 | 25 | 30 | 16 | 11 | 82 | 33 |

| 52' | 176 | 59 | 64 | 24 | 19 | 166 | 26 |

| 53 | 60 | 20 | 22 | 9 | 6 | 57 | 26 |

| 53' | 76 | 21 | 27 | 11 | 10 | 69 | 31 |

| 54 | 88 | 35 | 38 | 14 | 16 | 103 | 29 |

| 54' | 60 | 22 | 20 | 8 | 9 | 59 | 29 |

| 57 | 61 | 22 | 20 | 7 | 11 | 60 | 30 |

| 57' | 170 | 47 | 54 | 24 | 19 | 144 | 30 |

| 58 | 128 | 37 | 55 | 14 | 10 | 116 | 21 |

| 58' | 144 | 38 | 64 | 16 | 15 | 133 | 23 |

| Firsts | 433 | 139 | 165 | 60 | 54 | 418 | 27 |

| Seconds | 626 | 187 | 229 | 83 | 72 | 571 | 27 |

| +-------+-----+------+-----+-----+-----+----+

| Total | 1,059 | 326 | 394 | 143 | 126 | 989 | 27 |

+------------+-------+-----+------+-----+-----+-----+----+

FORKED.

On November 19, 1912 there appeared in a stock of a double recessive

eye-color, vermilion maroon, a few males which showed a novel form of the

large bristles (macrochaetae) upon the head and thorax. In this mutation

(text-fig. E) the first of several which affect the shape and distribution

of the bristles, the macrochaetae, instead of {58} being long, slender, and

tapered (see Plate 1, fig. I), are greatly shortened and crinkled as though

scorched. The ends are forked or branched, bent sharply, or merely

thickened. The bristles which are most distorted are those upon the

scutellum, where they are sometimes curled together into balls.

LINKAGE OF VERMILION AND FORKED.

[Illustration: FIG. E.--Forked bristles.]

Since forked arose in vermilion stock, the double recessive for these two

sex-linked factors could be used in testing the linkage relations of the

mutation. Vermilion forked males were crossed to wild females and gave

wild-type males and females, which inbred gave in F_2 the results shown in

table 39. Forked reappeared only in the males in the following proportion:

not-forked [female], 742; not-forked [male], 346; forked [male], 301. The

result shows that the character is a sex-linked recessive.

TABLE 39.--_P_1 wild_ [female] [female] x _vermilion-forked_ [male] [male].

_F_1 wild-type_ [female] [female] x _F_1 wild-type_ [male] [male].