Progress on finding a gay gene

A new study has just been published that has some evidence that may support the gay “gene” (or “genes”) concept.

Some research has focused on a number of different areas of human biology. Such diverse areas as brain anatomy, brain physiology, male children’s birth order, mother’s genetic makeup, psychology, social interactions and others, may play a role.

For example, some researchers have found differences in certain physical structures in the brains of straight and gay men. Structures that seem to be different may be the anterior commissure, massa intermedia, suprachiasmatic nucleus and other areas of the hypothalamus.

Other research has shown that birth order of male children in the same family seems to be linked to an increasing chance of later-born children being gay.

Xq28

In the early 1990s some research on the genetics of gay male brothers showed that gay men had more gay uncles and cousins on the maternal side of their families than they did on the paternal side. This implied that there might be a gene on the X chromosome (inherited only from the mother) that was causing some of these men to be gay. Further testing showed that there was an area of X chromosome (Xq28) that was found in a much higher percentage in gay brothers than would be expected. Over the next 20 years, some studies confirmed this result, but a few got significantly different results. And at least one small study showed the opposite result. There’s been some controversy as to whether there is a gay gene, and if so, is it on the X chromosome in the area of Xq28.

Chromosomes 7, 8 and 10

Human chromosomes, by Steffen Dietzel.

Human chromosomes, by Steffen Dietzel.

As research continued, other areas of different chromosomes were implicated as being involved in determining whether an individual male child developed a gay or straight sexual orientation. Some areas of chromosomes 7, 8 and 10 may also contribute to the cause of being gay. Interestingly, some animal studies have shown that a related area of the X chromosome in those animals predisposes to gayness as well.

The most recent study: Xq28 and Chromose 8

The most recent study used a large number of gay brothers and looked closely at their genetic makeup. The findings showed that a discrete area of the X chromosome (Xq28), and a portion of chromosome 8, seemed to predispose to their gayness.

The authors of the study concluded:

Results, especially in the context of past studies, support the existence of genes on pericentromeric chromosome 8 and chromosome Xq28 influencing development of male sexual orientation.

But the statistical analysis doesn’t conclusively demonstrate that the correlation is true. Therefore it doesn’t prove that this particular genetic combination is the cause of homosexuality. But it may suggest that they play a role in determining sexual identity. Perhaps the interactions of the products of these genes predisposes to one’s becoming gay.

While it would be convenient to think that the cause of someone’s sexual orientation might be entirely genetic, research indicates that other factors (biologic, social, psychological, etc.) may still play a role.


Mark Thoma, MD, is a physician who did his residency in internal medicine. Mark has a long history of social activism, and was an early technogeek, and science junkie, after evolving through his nerd phase. Favorite quote: “The most exciting phrase to hear in science... is not 'Eureka!' (I found it!) but 'That's funny.'” - Isaac Asimov

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