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Show 1903.] IN FANCY MICE AND RATS. 85 the blw. cS a the albino gametes equalled the browns and the blacks collectively, for with various albinos he gave 27 coloured {q.v.), 31 albinos, a near approach to equality. As regards the brw. o* y, the evidence is that with 3 albinos he gave 11 coloured, 19 albinos. On the other hand, 4 heterozygous coloured females x w . cS e gave 16 coloured, 7 albinos. As the result of the reciprocity of these numbers, the total (adding expt. 23) of coloured to albinos, produced by all matings in the form D R x R, is exactly 59 to 59. It is, however, difficult to believe that the departure from equality just named is simply fortuitous, for it is in each case steadily maintained through a series of families. If the figures are grouped according to mothers (instead of fathers, as here) these peculiarities are partly lost, but further experiment may possibly indicate that different kinds of heterozygotes are here to be distinguished. Of matings in the form D R x D R there are ten cases, expts. 26-7, 32-4, 37-8, 42-4 giving a total of 49 coloured, 14 albinos, the simple Mendelian expectation being 47"25 to 15*75. In these experiments there is also good evidence of the appearance of dominants containing no albino, for example brw. o* (C2-2), and probably blw.C1. Information given me by Mr. J. Wilson Steer and Mr. Atlee, and the experiments lately begun by Miss Durham and Mr. Staples Browne, enable m e to add a few indications as to the probable specific behaviour of some of the colour-types in crossing, though these have at present only the value of hints for further experiment. The agouti {Mus musculus colour) is of course dominant to albino, but so far has not been resolved in F„, having apparently the same behaviour as the wild colour in Cuenot's experiments. but sometimes piebalds of agouti and white appear. Yellow and black crossed have given sables or " dingy fawns."* Chocolate x albino may give, according to Mr. Steer, the wild musculus colour, doubtless by reappearance of the black pigment in association with brown of the chocolates. Probably the strains used had other differences also {cf. p. 97). Miss Durham has found chocolate a simple dominant over albino. Sable X black-and-white, according to the same authority, has given sables, though in this case the result will probably be found to differ according as the black-and-white is homo- or heterozygous. Sables bred together have given sable, black, and clingy fawn in the same litter. Blue X albino has given a full black, sometimes with white patches on tail. Two yellows (from an inbred strain 4 years old) gave 1 yellow and 2 chocolates {Steer). This last occurrence is unexpected and needs careful verification. * More recently Miss Durham has thus bred some full blacks. Reliable and extensive information as to the result of mating: yellows with blacks is greatly needed. |