Within the last decade, genetic analysis of heritable traits has taken a huge step forward with the advent of DNA microarray technology. Using this technology, it is possible to scan large lengths of the human genome (even an entire genome wide scan—GWAS) for numerous individuals, at quite reasonable costs. This DNA microarray technology has led to the discovery of genes that are associated with complex diseases, such as Crohn's Disease. If homosexuality truly has a genetic component, DNA microarray studies would not only definitively prove the point, but would identify specific gene(s) or loci that might be associated with those who express a homosexual orientation. The first attempt to do genome wide scans on homosexual males was done by Mustanski et al. in 2005.42 The results suggested possible linkage near microsatellite D7S798 on chromosome 7q36. However, an attempt to repeat the finding (along with ~6000 well-defined SNPs spread comparatively evenly across the human genome) failed to find any significant SNPs.43 However, a third study using Chinese subjects found a weak association at the SHH rs9333613 polymorphism of 7q36.44 A more general study, examining mate choice among different populations, found no genetic link, prompting the investigators to speculate that such choices were "culturally driven."45 The largest genome wide scan was conducted by 23andMe. 7887 unrelated men and 5570 unrelated women of European ancestry were analyzed by GWAS. Although unpublished, the data was presented at the American Society of Human Genetics annual meeting in San Francisco, showing that there were no loci associated with sexual orientation, including Xq28 on the X chromosome.46 So, the preliminary studies on possible genetic causes of homosexual orientation tends to rule out any dramatic genetic component to sexual orientation.
reference :
Mustanski, B. S., Dupree, M. G., Nievergelt, C. M., Bocklandt, S., Schork, N. J. & Hamer, D. H. 2005. A genome-wide scan of male sexual orientation. Hum. Genet. 116, 272–278 (2005).
Ramagopalan, S. V., D. A. Dyment, L. Handunnetthi, G. P. Rice and G. C. Ebers. 2010. A genome-wide scan of male sexual orientation. J. Hum. Genet. 55: 131–132.
Wang, B., Zhou S., Hong F., Wang J., Liu X., Cai Y., Wang F., Feng T., and Ma, X. 2011. Association Analysis Between the Tag SNP for Sonic Hedgehog rs9333613 Polymorphism and Male Sexual Orientation J. Androl. 2011 Sep 22.
Laurent, R., B. Toupance, and R. Chaix. 2012. Non-random mate choice in humans: insights from a genome scan. Molecular Ecology 21:587–596.
E. M. Drabant, A. K. Kiefer, N. Eriksson, J. L. Mountain, U. Francke, J. Y. Tung, D. A. Hinds, C. B. Do 23andMe. 2012 Genome Wide Association Study of Sexual Orientation in a Large, Web-based Cohort. Abstract presented at the American Society of Human Genetics annual meeting in San Francisco.