Genes, plants, and people : essays on genetics / by C.D. Darlington and K. Mather.

  • C. D. Darlington
Date:
[1950]
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Genes, plants, and people : essays on genetics / by C.D. Darlington and K. Mather. Source: Wellcome Collection.

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    GENES, PLANTS AND PEOPLE phenotype. And there are many who refuse to believe that visible agents are sufficient to effect visible results and that there is not something else behind the chromosomes which will permit mystical definitions of heredity and species. The reformation has been too profound to be accepted by those brought up in the old tenets. They prefer to halt between two opinions. 1Ъе most immediately obvious and direct conclusion from Mendel's work was that a new individual or zygote produced by fertilization owes its constitution directly and predictably to the germ cells or gametes which go to make it, and not to the parents which provide those gametes. A hybrid is, therefore, the product of the union of dis¬ similar gametes and not necessarily of dissimilar zygotes. Yet this definition is scarcely recognized outside experi¬ mental genetics to-day. In learning the properties of hybrids we have not merely discoA^ered the general laws of heredity and variation, we Ьал^е come to understand the nature of particular species. The troubled history of Œnotbera has been a struggle for fifty years between those who considered its forms as species and those who objected to them as hybrids. The solution came when it was realized that they were both. The paradox of the permanent hybrid then revealed how sex-chromosomes came about and how sex-determination developed in its multifarious ways. It must not be supposed, therefore, that the earlier development of genetics was smooth. The separation of breeding work and cytology led to many unfortunate results. Each technique has its own vices. Just as experi¬ mental breeding unrelated with cytology led de Vries and Bateson up several false trails, so cytology unrelated with experimental breeding led Roux to the struggle of the parts and Weismann to a theory of germinal selection, as he called it, in which all differentiation depended on a sorting out of determinants within the body during development. W^e find as late as 1911 Johannsen saying XX
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