9. EXCERPTS I: A Gay Gene?
Dean Hamer and associates have employed genetic profiling techniques to identify the chromosomal site of a putative male homosexual allele (gay gene). This technique has employed the well-known method of seeking marker alleles (DNA sequences associated with specific traits) that co-segregate among family members with that of homosexuality. The closer the marker is to the allele that gives rise to homosexuality on their shared chromosome, the more faithfully the two match each other in family inheritance. They have identified such a locus on the X chromosome, but have not yet identified the gene itself. There is some controversy about this claim, which was not confirmed in a separate study. Further research will be required, not only on the assignation but also on whether homosexuality is a product of a single gene. The location of an allele on the X chromosome precludes a contribution of fathers to the trait, so this leaves those cases that appear to have a paternal source unaccounted for. (p. 143) There is indeed some controversy Younger brother effect About 20% of gay individuals may have acquired their status as a consequence of a prior immune response between their mother and the Y chromosome of a fetal male from a previous pregnancy (Blanchard and Bogaert). The effect of the immunity may cover all later pregnancies. It may have skewed the estimates of frequency of homosexuality which had been presumed to be genetically linked. Immune responses can be potent and might give rise to strong effects on sexual orientation. Identification of gene New information has the potential to change our perception of the homosexual trait significantly. I currently have access only to a news presentation in Science (362: 385 2018) of a talk by the lead author, Andrea Ganna. The study covered questionnaires to half a million individuals of whom 26,000 had some degree of homosexuality and the investigators tentatively identified three regions of the genome in which variants correlated with same-sex experience; the site previously identified by Hamer on the X chromosome was not one of them. The most that can be extracted from this study is that no gay gene has been established. I will not pretend to be surprised or disappointed. The tenor of this book has been to argue that sexual orientation is a continuum, much like the heights of adults, and that it may be influenced by familiarity between couples. If I am right, the establishment of its genetic content will require a more nuanced understanding of its expression. One should not expect that homosexuality arises from a single source. There is already evidence that the gay trait may have either a paternal or maternal pedigree; the class of heterosexuals may encompass a very wide range of sexual preference; we may expect that sociality will be closely related to sexuality. It may be that geneticists are looking in the wrong place for homosexuality. Read my next blog (Predators) by clicking here. Read the full article
