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Gay-Straight Identical Twin Study Seeks to Find Gay Genes

By J. Titterton

Here's a big question for the gay community: Is it genetics or environment that causes our same-sex attraction? Well, life is never cut and dry, is it—it turns out it may be a combination of the two. The UCLA Center for Gender-Based Biology has launched a new study that aims to identify the genes responsible for sexual orientation and to understand how outside biological factors called epigenetics may influence how those genes express sexuality. Epigenetics refers to the biological effects that regulate which genes are turned on and off in the body and at what place in time.

But wait, haven't we already done gay twin studies? Well yes—but not quite like this. This new study looks at identical twins who share identical genetics—but not sexualities. The case studies are primarily of twins where one is gay and the other is straight, and attempts to see what differences in the genetic chain cause the diverging sexualities.

"This study is very different from traditional twin studies,” says lead scientist Dr. Sven Bocklandt of the David Geffen School of Medicine of UCLA. “Instead of simply calculating the role of genetics, we use these gay-straight identical twin pairs to actually identify genes that play a role in sexual orientation.”

Identical twins have long been used to study the role of genetics in a variety of traits, and with good reason—since identical twins share identical genetics, any deviation between them may in theory be traced to outside factors.

“Both twins have the same genes, but they might use these genes differently," says Bocklandt. "And that difference in gene use could explain the difference in sexual orientation. If we can identify specific genes that are 'turned off' or 'turned on' among our gay and straight twins, we will have excellent genetic targets for further investigation with respect to sexual orientation."

The connection between sexuality and genetics has become a hot topic in the scientific community in recent years, and recent studies have pointed increasingly to at least some connection between sexuality and genetics. Of course, for gay and lesbian people, the implications of these studies go beyond scientific curiosity. Politically, the finding of hard evidence supporting genetics' influence on sexuality would help put to rest the "sexuality is a choice" and "lifestyle" arguments of social conservatives. On the other hand, some in the gay community have expressed concern that if a "gay gene" or "genes" were found, scientists might look for a "cure" or "treatment" for it.

Be a Part of the Study
The UCLA Twins study has already recruited half of its participants, but is currently looking for more. Participation is easy: Both twins donate a saliva sample, fill out a brief questionnaire, and mail the study materials back to UCLA. Results of the study are expected later this year. Learn more at