When animals of the plus selection series are crossed with animals of
the minus selection series, an F₁ generation of offspring is obtained
which varies about a mean intermediate between those of the respective
uncrossed races. Thus, from an examination of Table 50 it will be seen
that when -2 animals of generation 6, minus series, were crossed with
+3.50 or +3.75 animals of generation 5, plus series, an F₁ generation
(Series 1) was obtained consisting of 93 animals of mean grade +0.06.
This generation is rather more variable than either uncrossed race, its
standard deviation being 0.71. The same is true of a second set (Series
2) of crosses made between a male of grade -3.25, generation 10, minus
series, and females of grade +3.75, generation 10, plus series. The 14
F₁ offspring are of mean grade +1 and have a standard deviation of 0.60.
(See Table 50, Series 2.)
In both the series of crosses summarized in Table 50, the F₂ generation
is more variable than F₁. In Series 1, 305 F₂ animals are recorded,
having a standard deviation of 1.01 as compared with 0.71, the standard
deviation of the F₁ generation. In Series 2, the F₂ offspring number 73
and have a standard deviation of 0.87, that of the previous generation
being 0.60.
The mean of the F₂ generation is very similar to that of the F₁
generation. In Series 1, the mean of F₁ is 0.06, and that of F₂ is 0.24;
in Series 2, the mean of F₁ is 1.00, and that of F₂ is 0.72.
It may also be seen from an examination of Table 50 that among the F₁
offspring produced by crossing the plus and the minus series there are
differences in transmission, as there are in the expression of the hooded
pattern. In general those F₁ individuals which are of high grade produce
offspring of higher grade than do their low-grade brothers and sisters.
This is exactly what has been observed in both uncrossed races.