Studies on inbreeding. III. The effects of inbreeding, with selection, on the sex ratio of the albino rat

Abstract

During the latter part of the nineteenth century it was generally believed that sex in man and in various animals is determined mainly by the amount of nourishment that the embryos receive; well nourished embryos were supposed to become females; those that were poorly nourished were assumed to develop into males.A considerable amount of evidence in favor of this view was collected by Diising ('83, '84, '86), who maintained, furthermore, that close inbreeding interferes with embryonic nutrition, by lessening the vitality of the mother, and so produces a great excess of male young.In the literature of the succeeding twenty years that deals with the subject of sex determination, Dusing's statement regarding the effect of inbreeding on the sex ratio was widely quoted and generally credited.Those who challenged the truth of the assertion were, in the main, advocates of the ancient theory, generally ascribed to Hippocrates (460-377 B.C.), that sex is determined in the ovary; eggs from the right ovary producing males and those from the left ovary developing into females.During this period three series of experiments were made that give data regarding the sex-proportions in a closely inbred stock.Huth ('87) inbred rabbits, brother and sister, for six generations and found a relatively low sex ratio (78.8 3 : 100 0 ) among the ninety young in which the sex was ascertained; Copeman and Parsons ('04) obtained a similar result in their inbreeding experiments with mice.Schultze ('03) concluded that inbreeding