con't. these genes code for protein subunits of glutamate membrane transport proteins. for the xq28 type of homosexuality, there is a distinct facial phenotype in dual expression. the xq28 gene is part of the melanoma associated antigen family of genes thats involved in surveillance against melanoma cancer. the xq28 gene (causes homosexuality, adhd, and autism) is in linkage with genes that increase female fecundity. that means, the genes that increase female reproductive success often are inherited with the xq28 melanoma cancer surveillance genes. when this is expressed in women, they statistically have more than 5 sexual partners during course of life. they produce many children. and, for these children, there is a 50% change for the women to pass the gene cluster to a son. this is good enough that evolution doesnt care about the small amount of gay sons, because the woman will produce many daughters that are evolutionarily more valuable. the frequency of xq28 allele in the 80s was around 6% of the female population. its about 8-10% today. this is also why adhd and certain types of high functioning autism increase at the same rate as male homosexuality. theyre all x-linked traits.  
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