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Dinesh

Dinesh club

Posted: 05 Feb 2023

Taken: 05 Feb 2023

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Genes, mitochondria, hormones etc

Genes, mitochondria, hormones etc
. . . .All women, O, are beautiful,” wrote Theodore Roethke, “when they are half-undressed” The same applies to Truth itself ~ Page 7 “HOMO MYSTERIOUS”

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 Dinesh
Dinesh club
There have been various plausible explanations for Haldane’s rule, en.wikipedia.org/wiki/Haldane%27s_rule though none of them can account for all cases, hence none of them is intellectually entirely satisfying. For example, sexual selection is stronger in males, which must compete among themselves for the attentions of females (technically there is greater variance in reproductive success between males and females, making male sexual traits more visible to selection). That in turn makes males more vulnerable to hybrid breakdown in a cross between different populations. The trouble is that this particular explanation does not explain why male birds are less vulnerable to hybrid breakdown than females.

Another difficulty is that Haldane’s rule arguably goes beyond mere sex chromosomes, which look parochial on a wider view of evolution. Many reptiles and amphibians don’t have sex chromosomes at all, but define their sexed on the basis of temperature; eggs incubated t a warmer temperature develop into males, or occasionally vice versa. In fact, given its apparently basic importance, the mechanisms of sex differentiation are perplexingly variable across species. Sex can be determined by parasites, or by the number of chromosomes or by hormones, environmental triggers, stress, population density, or even mitochondria. The fct that one of the two sexes tends to be worse affected in crosses between populations, even when sex is not determined by any chromosomes at all, suggests there might be a deeper me;chanism affot. Indeed, the very fact that the detailed mechanisms of sex determination are so variable, yet the development of two sexes is so consistent, implies that there could be some conserved underlying basis to sex determination (the process driving male or female development) which different genes merely embroider. ~ page 253

THE VITAL QUESTION
15 months ago. Edited 15 months ago.

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