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.
