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.

    57/469 (page 34)
    34 Structural Characters : Animals [ch. 43. Polydactylism occurred in a Guinea-pig, the off¬ spring of normal parents, and ran an irregular course in its subsequent descent (Castle, 49). Cat. 44. The abbreviated tail of the Manx Cat is a dominant (more or less imperfect) to the normal tail (see Anthony, 2 ; Hind, 151; Davenport, 98; Kennel, ibb,a). Godron (J/ém. Ac. Stanislas, 1865) records a similar observation in the Dog. 45. Polydactylism is almost certainly dominant ; but, as in other types, irregularities doubtless occur. Fowls. For the study of heredity Fowls are especially well suited. In addition to their many colour-characteristics the various breeds present a great range and variety of struc¬ tural features. Among the long series of offspring which hens of the more fertile breeds produce, the descent of these charac¬ teristics can be watched in families of ample length. The chief papers dealing with Fowls are R.E.C. (19-22); Hurst (156); Davenport (loi). The following is a list of the principal facts already elicited as to the behaviour of these structural features but much remains to be done. 46. Various shapes of comb, for example the rose comb and the pea comb, are both dominant to the single comb. The double or longitudinally split condition is also dominant to the unsplit. See pp. 61-7. Many of the finer details in regard to the heredity of comb-shapes are not yet clear. The classification of the comb-types in the newly-hatched chickens is generally very easy, but in occasional strains forms intermediate between the pea and the single occur in which may probably be due to subtraction-stages of the pea factor {q-v.). Some of the singles extracted in from various crosses have lateral sprigs—as, fanciers say. It is not impossible that these irregular processes are due to additional minor factors, but they are subject to so much fluctuation that their descent would be very difficult to trace. The comb of the Silky fowl is a rose, + a trifid element which causes its posterior end to be divided into three irregular points. In F^ from Silky x Single, regular rose combs are produced in those individuals which have the rose factor without this trifid element. Attention may be called to the dominance of the median splitting of the comb found in certain breeds, for the facts may have a bearing on the genetics of meristic characters. Splitting of the comb may occur in one of