Reports to the Evolution Committee of the Royal Society. 1-5.

Date:
1902-1910
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Licence: In copyright

Credit: Reports to the Evolution Committee of the Royal Society. 1-5. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

    121/526 (page 117)
    for finally answering this question in the case of the comh is not liefore us. It was not until the bearing of the Mendelian discovery was fully realised, and its applicability to these phenomena shown, that the absolute necessity for a decision on this point became evident. Moreover, until at the very least three successive generations have been hred the point cannot be quite decided. We may then usefully at this stage consider the facts briefly in the light of each of these two hypotheses, and point out how far either of these suppositions is consistent with observation. First Hypothesis: that every Recessive is, in composition, RB. According to this view the two original Brom. birds must be re- o;arded as of difierent composition, the ? giving x Leghorn LK ^ (Experiment 20), 18 p.c. and 0 s.c. is probably to be considered as pure dominant, DD. The ^, however, gave by three different Leghorn hens in P.c. S.c. Experiment 43 7 18 44 10 10 45 7 0 He would therefore be regarded as a dominant cross, DE. We note chat in Experiment 43 the numbers 7 : 18 are far from the expected 1 :1, being 1 : 25. To this point reference will again be made. The same ^, whose possible impurity was then luisuspected, bred (see table, p. 112) with I.G. BSE ? of undoubted purity, gave five Ijirds, of course all p.c. We expect, then, that of these half were DD and half DE. But all these five I.G.'s, when crossed with Leghorns, .;ave mixtures, as told in Experiments 45—58, the proportion of p.c. to s.c. being again very various, though, as a matter of fact, the totals, 122 p.c, 113 s.c, approach the expected equality. Five is a small number for such a test, still it is noticeable that none of them appeared to he DD, while on this hypothesis half should have been so. Of these five birds two were bred together, and, as told on p. 112, there was at once a mixture of peas and singles, 6 p.c, 6 s.c, the hypothesis expecting 3 p.c. : 1 s.c. Of these birds, unfortunately, two only, both p.cs., survived to be tested. Both were pure dominants DD, though DD : DE should here be 1 : 2. One of the five birds (I.G. ? 17) here assumed to be DE. with three Leghorn cJ's gave 48 p.c. and 41 s.c. (Experiments 49—51) closely approaching the expected equality. _ This hen was bred with I.G. Ed. ^J. As to the latter the evidence ts that he gave (Experiment 21) with a Leghorn ? 29 p.c. and 1 s.c, which is a close approximation to purity. With I. G. ? 17 he gave a family, all p.cs., of which one alone was tested, I. G. ? 37, proving (iixperiment 63) to be, on the hypothe.sis, DE, and giving x Leghorns