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Genetic materials human gets from his parents. Genes play very important role in determine of human's sexuality. Sexual determination essentially follows a default pathway where all embryos are female unless they inherit a male determining factor, thereby initiating a novel developmental pathway, which triggers the differentiation of testes from cells which would otherwise form ovaries…
J. Kallman's and W. W. Schlegel's findings in the 1940s showed that twins had a 100 percent concordance rate for homosexual orientation, where concordance is defined as the level of similarity existing for different characteristics. Although the results seemed overwhelmingly high, they laid the base for further studies. In 1991, J. Michael Bailey and Richard C. Pillard conducted a similar experiment comparing identical twins, fraternal twins, and nongenetically related adopted brothers. The genetics of sexual orientation are not quite so straightforward, but there is no doubt that becoming gay is influenced by a genetic predisposition. In one study, it was reported that 52% of monozygotic twins of gay men were also gay, but this figure dropped to 22% for dizygotic twins. (1)
Dr. Hamer in 1991 from the Department of Biochemistry at the national Institute of Health began a study - possible genetic natire of homosexuality. He chose to study markers on the X chromosome because there was already evidence for a preponderance of gay men on the maternal side of families. Hamer hypothesized the different ways that a genetic disorder could be expressed in a person. ...
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