Breeding and the Mendelian discovery / by A.D. Darbishire ... with illustrations in colour and black-and-white.

Darbishire, A. D. (Arthur Dukinfield), 1879-1915.

Date:: 1911

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

Credit: Breeding and the Mendelian discovery / by A.D. Darbishire ... with illustrations in colour and black-and-white. Source: Wellcome Collection.

352/370 (page 270)

$270 BREEDING 1:2:1 in the second hybrid generation, and so on— are, as it were, a secondary display set ofí by certain varietal characters becoming inherited by the sexual mode described in this paragraph. The heterozygote, together with the ordinary (or homozygous) type {xy + xx) first came into existence in connection with the inheritance of sexual characters. And it will readily be admitted that an extremely simple way of bringing about the production of the two sexes in equal numbers would be the institution of one sex (A), half of whose germ-cells contained the factors for one sex, whilst the other half contained those for the other ; and of another sex (B) all of whose germ-cells were indifíerentiated as regards sex. The original mode of inheritance, of which the Mendelian is a later development, and which has pos¬ sibly persisted without much modification as the sexual mode, may, therefore, be expressed in the formula— DR X RR = 50 % DR + 50 % RR Or, more generally— xy X XX — ЬО xy ЬО % XX ^ The familiar DD X RR I DR I I I I , 1 DD 2 DR 1 RR ! I J I)D 1 DD 2 DR 1 RR RR is a secondary development, and only appeared when$