It could not be tested at the time, but some evidence came from X chromosome methylation patterns in mothers of gay men.īocklandt later headed to the University of California, Los Angeles, and tested imprinting directly by comparing the entire genome’s epigenetic marks in male identical twins of whom one was gay and one straight. We illustrated this by suggesting how atypical imprinting of the X chromosome could lead to failure to inactivate feminising genes or activate masculinising ones, resulting in same-sex attraction in males.
That led me and graduate student Sven Bocklandt to hypothesise in 2003 that epigenetics may play a role.
Despite such work, it was clear that inherited differences in DNA could not account for all of the observed variation in sexual orientation.
