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Show 1903.] IN FANCY MICE AND RATS. 89 Lastly two pairs gave both greys and yellows, thus:- Pair Patches. Grey. Yellow. XII 2 3 LXXXIY 5 4 In the original account and in the discussion of the facts by Professor Weldon in ' Nature,' the offspring of the 29 families are referred to as having consisted of a mixture of greys, yellows, and blacks; and the fact that only certain families gave blacks and certain families yellows, and that no family gave both blacks and yellows, is not emphasised. We can conceive that both yellows and blacks might be associated with greys when " fawns " are crossed with albinos, but till the phenomenon occurs it need not be considered in this connection *. To proceed with the fundamentally important question of the purity of the coloured race, we are informed t>hat the original waltzers were bred together for some months and gave only offspring like themselves. The number of individuals thus tested and the number of offspring raised from them are not given, but we may conclude that they were considerable. When, however, we regard this evidence of purity in the light of the facts provided by the six families which gave either yellows or blacks, we perceive that if " fawn " is dominant to yellow and to black, the occurrence of yellows and blacks in the crosses with albino is readily explained. W e have in fact only to suppose that in family 27 the coloured mother, and in families 77, 78, 85 the coloured fathers, contained black; and that in families 12 and 84 the coloured fathers contained yellow; and the results are fairly clear. The chance of seeing the impurity by merely crossing-fawns together would not be very great. Most of them evidently were pure, and since black x yellow certainly may give a clingy fawn heterozygote, the impurity would probably not be demonstrated unless fawns containing black bred together, or fawns containing yellow bred together. By breeding the mother of family 27 with the father of 77, 78, or 85, some test of this suggestion might have been made. Of course we have as yet no direct experimental proof that fawn is dominant to black and to yellow; but since sables can throw blacks, and since in rats grey-and- white is dominant to black-and-white, it seems very possible that these " fawns" may also have been thus dominant. * When a compound character is crossed with a recessive, it sometimes happens that components of the compound appear already resolved in members of Ft. For example, I have seen the " walnut" comb of the pure Malay fowl (which can be produced by synthesis of rose-comb and pea-comb in a more or less stable union) crossed with single comb give some rose, some pea, some walnut, as well as some single. Such a phenomenon will probably be demonstrated to be a partial monolepsis (" false hybridism"), and zygotes exhibiting the several components will probably not reproduce the excluded elements in their posterity. |
