What does your mom’s X chromosome have to do with being a gay son?

Women have two X chromosomes, men have an X and a Y chromosome. We all know this, right? What do women do with two X chromosomes? Well, one of them is inactivated in each cell. Not necessarily the same one either. Some women have higher X chromosome inactivation ratios than others. The one’s that do, have an increased probability of having a gay son. How much more?  

Hum Genetics. 2006 Feb;118(6):691-4. Epub 2005 Dec 21.

Extreme skewing of X chromosome inactivation in mothers of homosexual men.

Bocklandt S, Horvath S, Vilain E, Hamer DH.

Department of Human Genetics, University of California-Los Angeles, Los Angeles, CA, USA. sbocklandt@mednet.ucla.edu

Human sexual preference is a sexually dimorphic trait with a substantial genetic component.

Linkage of male sexual orientation to markers on the X chromosome has been reported in some families.

Here, we measured X chromosome inactivation ratios in 97 mothers of homosexual men and 103 age-matched control women without gay sons.

The number of women with extreme skewing of X-inactivation was significantly higher in mothers of gay men (13/97=13%) compared to controls (4/103=4%) and increased in mothers with two or more gay sons (10/44=23%).

Our findings support a role for the X chromosome in regulating sexual orientation in a subgroup of gay men.

PMID: 16369763 [PubMed – indexed for MEDLINE]