Heredity : in the light of recent research / by L. Doncaster.

  • Doncaster, L. (Leonard), 1877-1920.
Date:
1910
Catalogue details

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

Credit: Heredity : in the light of recent research / by L. Doncaster. Source: Wellcome Collection.

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    П] HEREDITY 129 in more than one allelomorphic pair, all possible combinations can be produced, except that no germ- cell can contain both the members of one pair. The suggestion that this segregation of chromo¬ somes, which can be seen to take place, is the mechanism by which the members of an allelo¬ morphic pair of characters are segregated, is quite speculative; but it seems exceedingly unlikely that machinery so exactly adapted to bring it about should be found in every developing germ-cell, if it had no connexion with the segregation of characters that is observed in experimental breeding. There is also the further fact in support of the suggestion, that it is known in many insects that one pair of chromo¬ somes is closely connected with sex, for in the males of these species one chromosome of the pair is absent or much reduced, but in the female both are similar. These sex-chromosomes separate from one another like the others (when both are present), and it has been seen that there is experimental evidence for the view that the sex-determiners behave like Mendelian allelomorphs. One serious difficulty however suggests itself at once ; the chromosomes are limited in number, and it is undoubted that more allelomorphic pairs of characters may exist in a species than there are pairs of chromosomes, although in such cases there is no evidence that members of different pairs are always associated together. Several suggestions have been D. 9