[1] The investigation of this remarkable family was made originally by
Cunier. The facts have been reexamined and the pedigree much extended by
Nettleship. The numerical results are somewhat irregular, but it is
especially interesting as being the largest pedigree of human disease or
defect yet made. It contains 2121 persons, extending over ten
generations. Of these persons, 135 are known to have been night-blind.
In no single case was the peculiarity transmitted through an unaffected
member. It should be mentioned that for night-blindness such a system of
descent is peculiar. More usually it follows the scheme described for
colour-blindness. It is not known wherein the peculiarity of this family
consists.
[2] We have knowledge now of seven colour-blind women, having, in all,
17 sons who are all colour-blind. Most of these cases have been
collected by Mr Nettleship.
[3] An alternative and perhaps more satisfactory interpretation of the
same facts has been proposed by Doncaster (_Jour. Genetics_ I, Pt 4, p.
377). Until more progress has been made with the analysis of sexual
differentiation it is not possible to decide which of the two
interpretations is correct. The numerical results predicted on both
systems are the same; but by introducing a more complicated though quite
reasonable formula for the representation of the sex-differences
Doncaster's method shows that colour-blindness may be a _recessive_ due
to the absence of a factor which produces normal colour-vision.
Cambridge:
PRINTED BY JOHN CLAY, M.A.
AT THE UNIVERSITY PRESS.