This thing called life

International day against homophobia: can you really breed out the homosexuality gene?

David Yu

Today is the International Day Against Homophobia. Actually, it is the evening of IDAH and I am trying to understand why anyone would be For Homophobia.

I keep thinking about a suggestion I heard on the radio from a homophobe with a long term view. He thought we should encourage same sex marriage because those couples would remain childless, and homosexuality would be bred out of the human species.

If I could convince everyone that this plan could work, would homophobes join the cause for same sex marriage? As a geneticist I would like to give it a good old tongue in cheek try.

The first observation that must be made is that all homosexuals have both a male and a female parent. We have to explain why most people who are passing on homosexuality are themselves unaffected and clearly heterosexual. Several explanations are possible.

Homosexuality might be a recessive trait, so that you have to have two copies of the particular gene (technically, an allele) to be gay. That means your parents are straight because they have only one copy. In this case it does not affect them because straight is dominant.

Or homosexuality could be co-dominant. I like to think that bi-sexuality is co-dominant, all balanced and binary. Instead of just straight vs. gay, there would be three phenotypes. You might have straight, bent and more bent. Or likes boys, likes girls, likes both.

We could have variable expression of the trait, with different outcomes depending on gender. A gene that makes a girl like girls might make a boy like girls even more than usual. This would mean that the lesbian gene is spread largely by men who love women a whole lot. A gay gene would then be causing rampant heterosexuality.

But the most interesting situation would be if homosexuality were caused by a dominant allele. This would give us the best chance to breed it out. The problem with this hypothesis is that when the allele is dominant, the parents of affected individuals are always affected too. All homosexuals would have at least one homosexual parent, and that is apparently not the case.

The only way the gay gene could be dominant is with incomplete penetrance. Stop laughing. I know that sounds funny, but ironically, it is the only thing I have said so far that could actually be true.

Incomplete penetrance is a real genetic term that provides a way to wriggle out of the dominance dilemma. Under incomplete penetrance, some people who carry the dominant allele are nevertheless functioning heterosexuals. They are so deep in the closet that they don’t even know it themselves.

The best scenario for reducing the frequency of a trait is for it to be dominant, and for its expression to result in no offspring production. Amazingly, these conditions can be met for homosexuality. All that has to happen is for every homosexual to accept themselves early, marry young, and stay faithful to their partner. True love is the answer.

Incomplete penetrance, however, is still a problem. (It always is, somehow, especially if you have to teach it to teenagers). It could mean that potential homosexuals are indulging in heterosexual behaviour. It is possible that the environment could play a role, for example, when society makes it easier to bring home someone of the opposite sex.
We need to encourage more people to express their latent homosexuality. It would help the cause if we embrace same sex marriage, celebrate true love in all its forms, and make homosexuality super cool.

If that makes you feel squeamish, just remember that you could have the last laugh. In the long term, it could reduce the incidence of homosexuality. In the short term, it will just reduce sorrow and suicide and the need for birth control.

By the time I publish this it will no longer be International Day Against Homophobia. Is this the end of the rainbow, or the beginning?

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