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The Search For a "Gay Gene"

Quest Finds Few Solid Answers, Opens Up Debate Over Its Merits
by Megan Hall

Many people think of homosexuality as it is portrayed on television shows such as "Ellen" and "Will and Grace." Few people understand the issues that homosexuals deal with in accepting their own sexual orientation and coming out to other people. Still, understanding the biological origins of homosexuality continues to be a topic of mainstream discussion. One of the larger debates focuses on whether homosexuality is a matter of genetics or of upbringing. This question has been a hot topic in recent years, and has prompted a number of studies, including the hunt for the elusive "gay gene."
Discovering the "Gay Gene"
In 1991, Michael Bailey, a psychologist in Illinois, noticed that a full 52% of identical twins of gay men he studied also identified themselves as gay. For fraternal twins, the number drops to 22%. Could it be that this correlation indicates a genetic event? Since identical twins possess the same genetic material (identicals share one egg; fraternal twins do not) and more identical twins share the same sexual orientation, then it seems logical that homosexuality might have genetic origins. Dean Hamer, a scientist at the National Cancer Institute, took this information and decided to examine the X chromosome in a new group of twins. Why the X chromosome instead of the others? Each cell has 23 pairs of chromosomes, long spaghetti-like strands of a huge molecule called DNA. The DNA is housed in the cell nucleus; if your cell is the "body," then the nucleus is the "skull," and the DNA is the "brain." It is DNA that tells the cell what to do. It does this through genes; genes are like codes in the DNA that the cells can decipher. All of the information about a person - hair color, eye color, height, gender - is contained in the genes. Gender is determined by the sex chromosomes; females have two X chromosomes and males have one X and one Y chromosome. So, if each parent passes one of this pair of chromosomes on to offspring, women can only pass on an X chromosome, while men can pass on either an X or a Y chromosome. How does this apply to Hamer's group of twins? The group he studied all had relatives on the mother's side that identified as gay. Since the mother can only pass on the X chromosome, he reasoned that perhaps there was something - a gene - on the X chromosome that contributed to their sexual orientation. To find out, Hamer examined the X chromosome of 40 pairs of gay brothers who had maternal relatives who also identified as homosexual. He did this by looking at markers (genetic road signs) on the X chromosome to see if the group of identical twin gay brothers had more of the same road signs than the group of fraternal twins. He found that this was true; the group of identical twin gay brothers did share a number of these chromosomal road signs - more than would be expected by chance and more than the group of fraternal twin gay brothers. His research team repeated this study with a new group of 33 gay brothers to verify it, and in 1995 published the same finding. This is called "linkage" - being gay is "linked" to having these road signs on the X chromosome. So, it looks like there really is a gene on the X chromosome that would influence sexual orientation, right?
Refuting the "Gay Gene"
Not so fast. For this finding to be considered scientifically valid a second team of researchers must independently replicate it. George Rice and George Ebers, both at the University of Western Ontario, used a separate group of 52 pairs of gay male identical twins - the same type of twins used in Hamer's study. In 1999, Rice and Ebers revealed that they were unable to see the same correlation between DNA road signs and gay twins. In other words, Hamer's group said, "if you are gay, then you are more likely to have these road signs on your X chromosome," whereas Rice and Ebers said, "if you are gay, you are no more likely to have these road signs on your X chromosome." Hamer says there's a gene there, Rice and Ebers say there isn't.
What to make of the conflicting results?
Hamer argues that Rice and Ebers didn't use only gay brothers with maternal gay relatives. This means that these gay brothers might have had other influences on their X chromosome besides a gene. This is actually quite possible; it is unlikely that there is one single influence affecting sexual orientation. In fact, no one has ever identified a gene responsible for a personality trait, and some argue that homosexuality is based more on environment than on genetics. The linkage Hamer found could be just one of many factors, one which happens to be on the X chromosome. The lack of linkage from Rice and Ebers's group could mean any number of things, that there is no genetic basis, that one hasn't been identified yet, or that there are other factors at work. Most likely there are.
Who's Correct?
Possibly both groups. Rice and Ebers argue that there is negative "selective pressure" against such a gay gene. Think about it: if this hypothetical gay gene showed up in a group of people, they would be less likely to reproduce (without artificial means), as same-sex couples are physically unable to produce a child. If they don't reproduce, they won't pass the gene on; the gene will then "commit suicide" by disappearing when these people die. But gays and lesbians are still capable of having children, just not with each other. Perhaps the presence of a gay gene enhances the action of a second gene (like a "nurturing" gene) which in turn lends the gay gene an overall positive selective pressure. This scenario would support Hamer's findings that a gene or gene cluster influences sexual orientation. But this hypothetical gay gene is presumably not limited to the children of gays and lesbians; heterosexual parents can have gay children as well. There has been no evidence to date that homosexual parents are more likely to have homosexual children. So there is no clear answer at this point. Hamer's results point to the possibility of a gay gene or gene cluster on the X chromosome, while Rice and Ebers' work refutes this result. Now both groups are continuing to look for the presence of genes using the road signs discussed earlier - Hamer on the X chromosome, Rice and Ebers on other chromosomes.
Problems and Implications
In the absence of a solid answer, we can begin to discuss the problems of the hunt for a gay gene. One problem with the studies is that they were performed on a group of gay men. No women were included in either study. If there is a gene on the X chromosome, and women have two X chromosomes (one from her mother, one from her father), it might be easier to look for this in women who identify as lesbians with maternal relatives who also identify as gay. If a gay gene is identified on one X chromosome, that chromosome can be further identified as having come from the mother or father. (Each of a woman's cells has only one active X chromosome, with this active chromosome deriving from the mother in half of her cells and deriving from the father in the other half. -Ed.) Another problem with these studies is that it's difficult to isolate individual factors - especially genetic factors - that may contribute to being gay. It's like trying to figure out the genetic basis for why some people are naturally cheerful and some are naturally gloomy. How do you separate the genetics (which may be horribly complicated) from environmental effects? Are environmental effects even involved? These are difficult questions to address. There are also ethical issues that come with the search for a gay gene. Many gays and lesbians are against this line of research. This may seem counter-intuitive at first until you begin to look at the implications. Why even bother searching for a gay gene? It hints that being gay is something genetically "wrong" and could lead to increased feelings of homophobia (fear of homosexuals), even discrimination and hate crimes. There is also the threat of pre-natal testing for the gay gene should one be discovered. Pregnant women could be tested for a gay fetus the same way they are tested for a fetus with Down's Syndrome - again implying that being gay is a disease. Would this then lead to an increase in abortions over something as harmless as sexual orientation? It's a scary thought. Others argue that discovery of this hypothetical gay gene would actually decrease feelings of homophobia and hate. If there is a biological reason for being gay, some might let go of the idea that gay people can be "cured" with rehabilitation or counseling, both of which have consistently failed at "changing" homosexual people to heterosexuality. Imagine heterosexuals undergoing counseling to change their orientation to homosexuality! Research on the origins of homosexuality is definitely controversial. Hopefully society will come to terms with the ongoing existence of homosexuals, and accept them as positive additions to the population regardless of whether or not there is a "gay gene." It is certainly going to be a long discussion, one with many different answers and many associated issues.
Megan Hall is a graduate student in the UCLA Department of Microbiology and Molecular Genetics.

	The Search For a "Gay Gene"

	Quest Finds Few Solid Answers, Opens Up Debate Over Its Merits by Megan Hall Many people think of homosexuality as it is portrayed on television shows such as "Ellen" and "Will and Grace." Few people understand the issues that homosexuals deal with in accepting their own sexual orientation and coming out to other people. Still, understanding the biological origins of homosexuality continues to be a topic of mainstream discussion. One of the larger debates focuses on whether homosexuality is a matter of genetics or of upbringing. This question has been a hot topic in recent years, and has prompted a number of studies, including the hunt for the elusive "gay gene." Discovering the "Gay Gene" In 1991, Michael Bailey, a psychologist in Illinois, noticed that a full 52% of identical twins of gay men he studied also identified themselves as gay. For fraternal twins, the number drops to 22%. Could it be that this correlation indicates a genetic event? Since identical twins possess the same genetic material (identicals share one egg; fraternal twins do not) and more identical twins share the same sexual orientation, then it seems logical that homosexuality might have genetic origins. Dean Hamer, a scientist at the National Cancer Institute, took this information and decided to examine the X chromosome in a new group of twins. Why the X chromosome instead of the others? Each cell has 23 pairs of chromosomes, long spaghetti-like strands of a huge molecule called DNA. The DNA is housed in the cell nucleus; if your cell is the "body," then the nucleus is the "skull," and the DNA is the "brain." It is DNA that tells the cell what to do. It does this through genes; genes are like codes in the DNA that the cells can decipher. All of the information about a person - hair color, eye color, height, gender - is contained in the genes. Gender is determined by the sex chromosomes; females have two X chromosomes and males have one X and one Y chromosome. So, if each parent passes one of this pair of chromosomes on to offspring, women can only pass on an X chromosome, while men can pass on either an X or a Y chromosome. How does this apply to Hamer's group of twins? The group he studied all had relatives on the mother's side that identified as gay. Since the mother can only pass on the X chromosome, he reasoned that perhaps there was something - a gene - on the X chromosome that contributed to their sexual orientation. To find out, Hamer examined the X chromosome of 40 pairs of gay brothers who had maternal relatives who also identified as homosexual. He did this by looking at markers (genetic road signs) on the X chromosome to see if the group of identical twin gay brothers had more of the same road signs than the group of fraternal twins. He found that this was true; the group of identical twin gay brothers did share a number of these chromosomal road signs - more than would be expected by chance and more than the group of fraternal twin gay brothers. His research team repeated this study with a new group of 33 gay brothers to verify it, and in 1995 published the same finding. This is called "linkage" - being gay is "linked" to having these road signs on the X chromosome. So, it looks like there really is a gene on the X chromosome that would influence sexual orientation, right? Refuting the "Gay Gene" Not so fast. For this finding to be considered scientifically valid a second team of researchers must independently replicate it. George Rice and George Ebers, both at the University of Western Ontario, used a separate group of 52 pairs of gay male identical twins - the same type of twins used in Hamer's study. In 1999, Rice and Ebers revealed that they were unable to see the same correlation between DNA road signs and gay twins. In other words, Hamer's group said, "if you are gay, then you are more likely to have these road signs on your X chromosome," whereas Rice and Ebers said, "if you are gay, you are no more likely to have these road signs on your X chromosome." Hamer says there's a gene there, Rice and Ebers say there isn't. What to make of the conflicting results? Hamer argues that Rice and Ebers didn't use only gay brothers with maternal gay relatives. This means that these gay brothers might have had other influences on their X chromosome besides a gene. This is actually quite possible; it is unlikely that there is one single influence affecting sexual orientation. In fact, no one has ever identified a gene responsible for a personality trait, and some argue that homosexuality is based more on environment than on genetics. The linkage Hamer found could be just one of many factors, one which happens to be on the X chromosome. The lack of linkage from Rice and Ebers's group could mean any number of things, that there is no genetic basis, that one hasn't been identified yet, or that there are other factors at work. Most likely there are. Who's Correct? Possibly both groups. Rice and Ebers argue that there is negative "selective pressure" against such a gay gene. Think about it: if this hypothetical gay gene showed up in a group of people, they would be less likely to reproduce (without artificial means), as same-sex couples are physically unable to produce a child. If they don't reproduce, they won't pass the gene on; the gene will then "commit suicide" by disappearing when these people die. But gays and lesbians are still capable of having children, just not with each other. Perhaps the presence of a gay gene enhances the action of a second gene (like a "nurturing" gene) which in turn lends the gay gene an overall positive selective pressure. This scenario would support Hamer's findings that a gene or gene cluster influences sexual orientation. But this hypothetical gay gene is presumably not limited to the children of gays and lesbians; heterosexual parents can have gay children as well. There has been no evidence to date that homosexual parents are more likely to have homosexual children. So there is no clear answer at this point. Hamer's results point to the possibility of a gay gene or gene cluster on the X chromosome, while Rice and Ebers' work refutes this result. Now both groups are continuing to look for the presence of genes using the road signs discussed earlier - Hamer on the X chromosome, Rice and Ebers on other chromosomes. Problems and Implications In the absence of a solid answer, we can begin to discuss the problems of the hunt for a gay gene. One problem with the studies is that they were performed on a group of gay men. No women were included in either study. If there is a gene on the X chromosome, and women have two X chromosomes (one from her mother, one from her father), it might be easier to look for this in women who identify as lesbians with maternal relatives who also identify as gay. If a gay gene is identified on one X chromosome, that chromosome can be further identified as having come from the mother or father. (Each of a woman's cells has only one active X chromosome, with this active chromosome deriving from the mother in half of her cells and deriving from the father in the other half. -Ed.) Another problem with these studies is that it's difficult to isolate individual factors - especially genetic factors - that may contribute to being gay. It's like trying to figure out the genetic basis for why some people are naturally cheerful and some are naturally gloomy. How do you separate the genetics (which may be horribly complicated) from environmental effects? Are environmental effects even involved? These are difficult questions to address. There are also ethical issues that come with the search for a gay gene. Many gays and lesbians are against this line of research. This may seem counter-intuitive at first until you begin to look at the implications. Why even bother searching for a gay gene? It hints that being gay is something genetically "wrong" and could lead to increased feelings of homophobia (fear of homosexuals), even discrimination and hate crimes. There is also the threat of pre-natal testing for the gay gene should one be discovered. Pregnant women could be tested for a gay fetus the same way they are tested for a fetus with Down's Syndrome - again implying that being gay is a disease. Would this then lead to an increase in abortions over something as harmless as sexual orientation? It's a scary thought. Others argue that discovery of this hypothetical gay gene would actually decrease feelings of homophobia and hate. If there is a biological reason for being gay, some might let go of the idea that gay people can be "cured" with rehabilitation or counseling, both of which have consistently failed at "changing" homosexual people to heterosexuality. Imagine heterosexuals undergoing counseling to change their orientation to homosexuality! Research on the origins of homosexuality is definitely controversial. Hopefully society will come to terms with the ongoing existence of homosexuals, and accept them as positive additions to the population regardless of whether or not there is a "gay gene." It is certainly going to be a long discussion, one with many different answers and many associated issues. Megan Hall is a graduate student in the UCLA Department of Microbiology and Molecular Genetics.