Archive for October, 2015

Are you Homosexual because of your Genes?

Do genes play a role in affecting the sexual orientation of person? This question was answered when results of two studies revealed that five markers attached to DNA can affect the sexual orientation of a person. However, the results of these studies have been disputed by several researchers. Andrew Gelman, who is a statistician at Columbia University in New York, claimed that the results of the study have been incorrectly presented. This criticism has been disputed by Tuck Ngun who is the co-author of one of the studies. However, he has admitted that the study was underpowered and added that he and his collaborators will soon issue a statement.

Background

The biology of sexual orientation of a person is one of the most hotly debated topics in human genetics. For the first time, studies have found a connection between markers attached to DNA and sexual orientation of a person. However, these markers can be influenced by external environment.

Studies

The studies provide strong evidence that genetics can have an impact on the sexual orientation of a person. For instance, when one identical twin is gay, there is a 20 percent chance that the other twin will also be gay. Since this rate is not 100 percent, it is assumed that environmental factors can have an impact on the sexual orientation of a person. An external factor that affects sexual orientation is the ‘Older Brother Effect’. It is believed that the chance of a man being gay increased by more than 30 percent for each older brother he has. Even though there are no studies to prove the existence of Older Brother Effect, many experts believe that this could be because of immune system reaction against male antigens which can affect foetus development.

To find out the link between genes and environment, geneticist Eric Viain conducted a study at University of California, Los Angeles. They studied the epi-genetic markers of the subject and tried to find the impact of the environment on these epi-markers. They collected DNA samples of 10 pairs of identical twins in which both were gay and 37 pairs in which only one twin was gay. When researchers scanned the epi-genomes of the gay twins, they found that 5 epi-markers were common among gays. Algorithm was developed based on these 5 epi-markers. This algo could correctly predict the sexual orientation of a person 67 percent of the time.

Limitations of this Study

Since this study took a small sample size of just 47 twins, the results of this study are likely to evaporate when test in a larger group. Another limitation of the study is that epigenetic markers present in the tissues of the body differ from those found in the brain. Since brain affects sexual orientation of person, researchers must study the epigenetic markers of the brain before coming to a conclusion

Critics of this study are of the view that just as genetic associations offer little insight into the sexual orientation of a person, little can be concluded from these epi-marks. These epi-marks are in regions that have not association with the gene of a person. For instance, one mark is associated with brain development, the second is located in the immune system, and the other 3 marks are in the areas that are not associated with any gene.

Most geneticists are of the view that genes have no impact on the sexual orientation of the person. Since, there are no ‘gay genes’, coming out with a conclusion that epi-marks affect the sexual orientation of the person may not be correct. The biggest study to find out the impact of genes on the sexual orientation of the person was conducted by Sanders. He took 409 pairs of gay brothers, including a few non-identical twins to find the effect of genes on sexual orientation of the person. They found that two areas of genome, namely chromosome 83 and X chromosome do impact the sexual orientation of a person. However, the exact impact of these chromosomes is yet to be determined.

Final Thoughts

Even thought the study conducted by Eric Viain is a step in the right direction, it is difficult to believe the findings of their study. There study appears incomplete and requires several changes before they can come to a definite conclusion. So do genes really affect the sexual orientation of person? We believe it does. However, there are limited studies to back our belief.