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[99] [100] As originally pointed out by Dean Hamer, [101] even a modest increase in reproductive capacity in females carrying a "gay gene" could easily account for its maintenance at high levels in the population. [100] In 2004, Italian researchers conducted a study of about 4,600 people who were the relatives of 98 homosexual and 100 ...
Studies of the X chromosome as well as the entire human genome have linked Xq28 to the heredity of homosexuality in human males. Xq28 is a chromosome band and genetic marker situated at the tip of the X chromosome which has been studied since at least 1980. [1] The band contains three distinct regions, totaling about 8 Mbp of genetic ...
The fraternal birth order effect does not apply to the development of female homosexuality. [13] Blanchard does not believe the same antibody response would cause homosexuality in firstborn gay sons – instead, they may owe their orientation to genes, prenatal hormones and other maternal immune responses which also influence fetal brain ...
Despite numerous attempts, no "gay gene" has been identified. However, there is substantial evidence for a genetic basis of homosexuality, especially in males, based on twin studies; some association with regions of Chromosome 8, the Xq28 locus on the X chromosome, and other sites across many chromosomes. [170
The fraternal birth order effect has been described by one of its proponents as "the most consistent biodemographic correlate of sexual orientation in men". [5] In 1958, it was reported that homosexual men tend to have a greater number of older siblings (i.e., a 'later/higher birth order') than comparable heterosexual men and in 1962, these findings were published in detail. [6]
The authors concluded that "our findings, taken in context with previous work, suggest that genetic variation in each of these regions contributes to development of the important psychological trait of male sexual orientation." It was the largest study of the genetic basis of homosexuality to date and was published online in November 2014. [60]
Variants of the androgen receptor (AR) gene have also been discussed, in that non-right-handedness in men has been linked with greater CAG repeats in the AR gene, which in turn is associated with lower testosterone. A theory that high prenatal testosterone leads to neuronal and axonal loss in the corpus callosum is supported by this hypothesis.
The idea of epigenetics and gene expression has been a theory applied to the origins of homosexuality in humans. One team of researchers examined the effects of epi-marks buffering XX fetuses and XY fetuses from certain androgen exposure and used published data on fetal androgen signaling and gene regulation through non-genetic changes in DNA ...