While genes rarely change over a lifetime, the epigenome is constantly changing. As such, they were better able to pinpoint which DNA methylation patterns might be associated with sexual orientation though this still proved hard.
Ngun’s study of twins doesn’t reveal how or when a male takes on the epigenomic marks that distinguish him as homosexual.
Despite this knowledge, scientists are still unable to find what determinant ultimately influences the development of the gene that affects sexual orientation.
“To our knowledge, this is the first example of a predictive model for sexual orientation based on molecular markers”, says first author Dr. Tuck C. Ngun, of the University of California-Los Angeles.
Study researchers told that out of 47 sets of identical twins studied, 37 were pairs, in which one twin was homosexual and the other was heterosexual.
In identical twins, DNA is shared and overlaps perfectly.
Their analysis generated a data set far too large for a team of humans to make sense of.
An algorithm they developed based on the five epigenetic markers could correctly predict the sexual orientation of men in the study 67 per cent of the time.
From this, the researchers identified DNA methylation patterns in nine small areas of the human genome that could predict whether each twin was heterosexual or homosexual with up to 70% accuracy. While identical twins have exactly the same genetic sequence, environmental factors lead to differences in how their DNA is methylated. “Simple correlations – if significant – of epigenetic marks of an individual with anything from favorite football player to disease risk does not imply a causal relationship or understanding”. Thus, by studying twins, the researchers could control for genetic differences and tease out the effect of methylation.
“It has always been a mystery why identical twins who share all their genes can vary in homosexuality”, Prof. But the existence of identical twin pairs in which only one is homosexual “conclusively suggest that genes don’t explain everything”, Bailey added.
However, other experts in the area say considerably more research will need to be done before the claims made by Ngun’s team can be backed up – with the study’s limited sample size a primary cause of concern.
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