However, it is not clear whether and how the genetic factors are expressed to simultaneously induce homosexuality in men and increased fertility in their mothers and maternal aunts, the researchers said.
Andrea Camperio Ciani of the University of Padova in Italy discovered mothers and maternal aunts of gay men tend to have significantly more offspring than those of straight men.
The study, scheduled to be published in the Journal of Sexual Medicine, said it appeared at least one gene on the X chromosome resulted in more men being gay and women having more children.
"Using questionnaires, we investigated fecundity -- fertility -- in 161 female European subjects and scrutinized possible influences, including physiological, behavioral and personality factors," Ciani said in a statement. "We compared 61 females who were either mothers or maternal aunts of homosexual men. One hundred females who were mothers or aunts of heterosexual men were used as controls."
The analysis showed both mothers and maternal aunts of homosexual men show increased fecundity compared with corresponding maternal female relatives of heterosexual men.
A two-step statistical analysis found mothers and maternal aunts of homosexual men had fewer gynecological disorders; fewer complicated pregnancies; less interest in having children; less emphasis on romantic love; placed less importance on their social life; showed reduced family stability; were more extraverted; and were divorced or separated from their spouses more frequently.