Epigenetic theories of homosexuality
Epigenetic theories of homosexuality concern the studies of changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence, and their role in the development of homosexuality. Epigenetics examines the set of chemical reactions that switch parts of the genome on and off at strategic times and locations in the organism's life cycle.
Source: Wikipedia — Epigenetic theories of homosexuality (CC BY-SA 4.0)