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Show 76 MR. W. BATES0N ON COLOUR-HEREDITY [May 26, inter se, and found that some pairs gave the expected mixture, while others gave dominants only. Qualitatively therefore the result is the normal one. It is not stated that the " extracted" albinos were tested, but there is little doubt that, in accordance with almost universal experience, they would have produced nothing but albinos. A leading fact illustrated by Cuenot's experiments, viz. the recessive nature of albinism, is borne out by the whole series of experiments under review. The fact is true of albinos in mice, rats, guinea-pigs * (Cumberland, 13 ; Castle, 7), and rabbits (Castle), so far as experiments have reached. Cases of the production of albinos by coloured rabbits {e.g. Polish by Dutch, albinos by silver-greys) are frequent in the fancier's literature. The contrary, the production of coloured animals by albinos, is not, so far as I know, illustrated by a single case, with the following exception. In the later editions of ' Fancy Mice ' (Upcott Gill), Dr. Carter Blake, formerly secretary of the Anthropological Institute, commenting on the statement that albino mice of whatever parentage produce nothing but albinos, writes (p. 16) that a pair of albinos produced some brown-and-white, some plum, some grey, and some albinos. If this result occurred under all precautions, it stands alone. Nevertheless we should be cautious in declaring the result impossible, for in Mendelian experiments the observer must be on the look out for the appearance of a character, elsewhere a definite dominant, as the consequence of crossing two dissimilar recessives. Not only may a dominant colour be produced by crossing two forms having a recessive colour,-e. g., purple flowers by crossing the white Datura Icevis with white D. ferox ; purple flowers in Sweet-Pea by crossing white " Emily Henderson" round-pollened form with the long-pollened form of the very same white variety ; purple flowers in the Stock by crossing two white varieties:-but also a dominant structural character, hoariness, may be produced by crossing glabrous (recessive) stocks of different colours, e. g., red and cream, or red and white t. In each of these cases the appearance of an atavistic character occurs as a consequence of the union of gametes bearing dissimilar characters ; but the character in which the reversion appears is of a class different from that in which the parental differentiation was seen. The same may very possibly be true of animals also. But in each of the cases known, the two varieties united, though alike bearing the same recessive character, differ obviously in some other respect; and we know that the cross-bred raised by their union is a heterozygote, i. e. a zygote formed by the union of dissimilar gametes. It is, I think, scarcely likely that Carter Blake's case of the mice is really to be so regarded, and on the whole the hypothesis of error is more probable ; but the possibility * Small " smudges " are said to occur irregularly in albino cavies, however pure. f This statement is based on results of experiments made by Miss E. R. Saunders as yet unpublished. |
