Poultry breeding : theory and practice / by A.L. Hagedoorn and Geoffrey Sykes.

  • Arend Lourens Hagedoorn
Date:
1953
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Poultry breeding : theory and practice / by A.L. Hagedoorn and Geoffrey Sykes. Source: Wellcome Collection.

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    Transgressive Yariabìiity iii along by the presence in every cell nucleus of certain genes. But it is certainly not true that it is scientifically defensible to speak of the gene for black or the gene for broodiness . The fact is that two very similar breeds, which show the same quality to the same extent, may be quite different in their genetic make-up, even as far as genes go which help to influence this quality in the same way. In all such cases, cross-breeding is a source of surprising variability. When we compare two popular and perfectly normal and Grammes 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 Fig. 18.—Size inheritance in a cross between Hamburg cock and Sebright bantam hen. Redrawn from Christian Wriedt's Heredity in Live Stock after Punnett and Bailey's experiments. productive breeds of fowls, we know that in each case the set of perhaps thousands of genes present makes normal harmonic development possible. But of course those two sets of genes may be differenti Cross-breeding and subsequent recombina¬ tion of differentiating genes may give us a number of quite novel, and often disharmonie and inferior combinations [Mjoen]. I have sometimes explained this unexpected disharmony by a mechanical parallel. When we have two perfectly good machines of some kind—typewriters of different make, or bicycles—the two machines of different make are both perfect, although their parts are not interchangeable. If we do try to interchange some of the minor parts, we seldom get another harmonic whole, a usable typewriter or bicycle. When we try breeding hybrid chickens together the result is