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Show 1903.] IN FANCY MICE AND RATS. 91 Before attempting further to analyse these facts, the results of wild-coloured Fx x albino must be given. In the body of the paper 88 young so produced are recorded, viz., 39 albino, 31 wild-coloured (18 darker, 13 lighter), 15 black, 3 yellow. The total increased subsequently to 205, of which 111 were albinos and 94 had some colour in their coats, the specific colours not being as yet given. All the coloured individuals from this mating were dark-eyed, as would be expected. In accordance with the other results we should expect- 105-5 albinos and 105*5 coloured with dark eyes, where experi- 1 -, -, -, q . ment gave J " " It is therefore clear that if we regard the gametes of FT as consisting of two kinds, colour-bearing and albino, in equal numbers on an average, this simple form of the Mendelian hypothesis fits the facts very closely, and the distribution of albinism and eye-colour is approximately what that hypothesis leads us to anticipate. When, however, we try to assign the ratios of the several colour-gametes to each other, and to determine the specific results of their unions, we encounter certain difficulties, though in all probability further experiment will enable us to make this analysis complete. So far we have no knowledge of the specific composition of the several types seen in F.„ and until they are bred separately inter se we can only predict the offspring with reserve. Any such prediction can only be made on the hypothesis that the regularity of the behaviour has been maintained, and that no original variation or mutation arises (as may happen for instance in peas and perhaps sweet-peas). W e must also expect some irregularities from the fact already mentioned, that the several families in Ft were not all comparable, and in subsequent generations it wdl be necessary to distinguish members of black-giving, or of yellow-giving families from the rest. Subject to these provisos, we expect the pink-eyed coloured types to give only pink-eyed when bred inter se and no albinos *, but that the dark-eyed Avill give both pink-eyed and dark-eyed; and that some of the offspring of dark-eyed mated inter se (or with albinos) will be albinos. The pink-eyed coloured forms mated with pure albinos will presumably give all dark-eyed offspring again f. Similarly taking the types of F2 singly, it is likely that dark-eyed yellows will give only yellows, perhaps creams, and albinos, * Unless the phenomenon seen in the albino guinea-pig occurs. f In M r. Darbishire's third report (28) just published it is recorded that a pink-eyed yellow-and-white in F 2 bred with albinos gave 8 albinos, 11 grey-and-white, 1 yellow-and-white. The occurrence of albinos from this mating is of course a proof that the constitution of the pink-eyed yellow was in this case not that suggested in the present text. Experiments with other coloured members of F 2 are not yet given. The relation of the yellows to the rest must be regarded for the present as quite unknown. It m a y be remarked that yellow-and-white varieties both of rabbits, fowls, and pigeons are often peculiar in their inheritance, and rarely breed true for many generations.-Jtdy, 1903.] |