PSYCH 3F03 Chapter Notes - Chapter 0: Extra-Pair Copulation, Estrous Cycle, Overdominance
10 Dec 2016
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Document Summary
Interest in explaining persistent low levels of human homosexuality stem from: evidence that homosexuals have lower lifetime offspring production, evidence that homosexuality is influenced by polymorphic genes. Twin studies indicate both genetic and environmental factors. Male homosexuality inherited more frequently from mothers side suggesting influence of polymorphic maternal effects/ polymorphic x-linked genes: homosexuality more common than can be explained by mutation- selection balance even if small fitness cost. Maternal effects: relationship between birth order and incidence of male homosexuality. Positively correlated with # of older brothers but not sisters. May be a result of different social environment experienced by younger brothers. Could also reflect progressive immunization of some mothers to male-specific antigens and the effect of this on sexual differentiation of the brain. Difficult to replicate: genome-wide qtl study indicated three autosomal genes that may influence male sexual orientation; also some support of xq28. Mechanisms for maintenance of polymorphism in genes that cause homosexuality: overdominance.
