Animal genetics / Frederick B. Hutt.

  • Frederick Hutt
Date:
[1964]
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Animal genetics / Frederick B. Hutt. Source: Wellcome Collection.

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    79 Intersexes, Sex Determination, and Sex Ratios Back in Chapter 7, where we considered sex determination and sex Hnkage, the reader was warned that the situation is not quite so simple as it was there presented, and that compHcations lay ahead. Here they come. They are very interesting, not just because sex is hardly a dull subject ( insofar as can be judged by the unusually rapt attention of my classes during lectures about it), but also because, after centuries of speculation about sex determination, including fifty years of genetics as a science, something new about sex determina¬ tion in mammals was learned as recently as 1959. That discovery was so long delayed for two reasons. In the first place, geneticists accepted somewhat too readily the concept that what the intersexes in Bridges' fruit flies had shown him about sex determination in Drosophila applied equally well to other species ( including all the mammals ) in which females are XX and males XY. We know now that it doesn't. In the second place, it was not until the newer techniques of cytology were applied to man and other mammals after 1950 that it became possible to learn much about the chromosomes of intersexes in such species. If, in species having heterogametic males, XY = $ , and XX = ? , how, then, do intersexes arise? Similarly if normal gametogenesis in the heterogametic sex results in the production of $ -determining and 5 -determining gametes in equal numbers, why then is the sex ratio at birth not always 1 : 1, instead of being, as in some mammals, 105 $ $ : 100 5 5 ? This chapter is written to answer these questions and others related to them. 421
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