Genetics Of Male Gender Identity
September 3, 2013

The Tricky Genetics Of Male Gender Identity

Brett Smith for - Your Universe Online

New research from scientists at Case Western University indicates that the development of gender in human males is somewhat tenuous and could point to a biological mechanism behind a spectrum of gender identities.

In the study, which was published in Proceedings of the National Academy of Sciences, scientists recruited volunteers from rare families in which a daughter has the same Y chromosome as her father.

All fetuses start development as a female, and females usually inherit an XX-pair of sex chromosomes – one from each parent. However, if a gene located on an inherited Y chromosome, called SRY, fails to trigger – the female-specific tissues will continue to develop, but they will become dysfunctional and infertile.

The new study focused on the SRY gene, which turned out to be relatively unreliable.

"A general principle of developmental biology is that evolution favors reliability," said study author Dr. Michael Weiss, a biochemist from Case Western. "Robust switches ensure that our genetic programs give rise to a consistent body plan to ensure that babies have one heart, two arms, ten fingers, and so forth."

Weiss and his colleagues said they wanted to better understand the connection between an XY-female and the SRY gene.

“The father has the same Y chromosome and the same mutation as the daughter," Weiss said. "And since he is a fertile male, we know that the switch must be poised right at its edge."

The team looked to determine the biochemical threshold necessary for flipping the SRY switch to initiate male development.

"Our expectation was that we'd find that a factor of 100 or more — a severe insult to the Y-encoded switch — was necessary to alter development," Weiss said. "But what we found was that the SRY threshold, as probed in father-daughter pairs, is only a factor of two."

This means that genetics cause human males to develop close to sexual ambiguity, unlike the genetic mechanisms behind other processes such as heart function. Researchers said a small deviation from the normal process could significantly alter sexual development in a growing fetus.

Despite the importance of sexual reproduction to a species, study researcher speculated that the tenuous nature of the SRY switch could be evolutionarily desirable, particularly in the light of changing attitudes toward gender identity.

"We have this tenuous switch on the Y chromosome, and we anticipate that its gift to humanity is variability in the pathway of male development from its earliest stages," Weiss said. "The essential idea is that our evolution has favored a broad range of social competencies. In prehistory, this range would have given a survival advantage to communities enriched by a diversity of gender styles."

Susan Case, a professor of organizational behavior who was not involved in the study, said her collegue’s argument was sound and noted that "diverse mixes of people offer more varied perspectives, more ideas and solutions, and more challenges to long-accepted views."

For example, in the corporate environment these differing styles and approaches can be leveraged to increase creativity, problem solving, or team robustness.

Perhaps even more controversial, the research seems to suggest that gender roles have a root in biology, the researcher noted.