Mendel's principles of heredity / by W. Bateson.

  • William Bateson
Date:
1913
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Mendel's principles of heredity / by W. Bateson. Source: Wellcome Collection.

    89/469 (page 64)
    б4 The Walnut Comb [CH. It was not a little surprising to see so striking and characteristic a structure as the walnut or Malay comb appear with strict regularity as the product of two such dissimilar parents as the rose and the pea. Not only is the general appearance of the walnut quite distinct from these, but the presence of the hairs constitutes a feature of absolute difference, for no hairs are found on combs of the usual types. Were the walnut, rose, pea, and single combs found as characteristics of wild birds no naturalist would hesitate to regard them as four distinct specific characters ; and even as the special properties of domesticated birds I suppose they would by many be regarded as evidence oí long-continued selection. Nevertheless, as will be seen, these four forms stand to each other in a simple genetic relation and the fact suggests wide possibilities in regard to many hitherto unexceptionable differences of specific value recognized among animals and plants. The interpretation of the facts was at first by no means easy, and I am sorry to have been responsible for the promulgation of a quite erroneous suggestion regarding them. Further knowledge of kindred phenomena has, however, made the elucidation of this case now perfectly clear and simple. To return to the experimental results. Having found that rose x pea gives walnut, the next thing to be done was to test the genetic properties of birds thus produced. This was done in two ways (i) by breeding the walnuts together, (2) by breeding them with singles. In what follows, the names may be abbreviated thus : R, rose ; P, pea ; RP, walnut ; and S, single. Experiment showed that RP x RP gave an family RP, R, P, and S. The appearance of S, which was not known to have been put in, is not at first sight intelligible. Repeated trials proved that the ratio in which these combs appeared was ()RP : 37? : 3/* : i^S. It was further proved by experiment that the R birds were either pure R or contained the recessive but gave no more P or RP ; that the P birds similarly could only give P, or P and 5 ; while the 5 were all pure to that character.