DNA methylation plays a significant role in gene expression and can be used as a predictive mechanism for physical characteristics such as sexual orientation. (Source: Wikimedia Commons, Christoph Bock)
Because sexuality is such a large part of headlines and advertisements, it is important to understand the biological basis of sexual attraction and sexuality. It is especially useful to be able to establish a connection between a person’s genes and his or her sexual preferences. Researchers at the David Geffen School of Medicine have attempted to do just that that; they have discovered an epigenetic mechanism that appears to be correlated with male sexual orientation. Their research furthers scientific understanding of human sexuality and how it may be linked to genetic mechanisms (1).
Each somatic cell in the human body is comprised of roughly three billion base pairs of DNA. The base pair is the functional unit of the human genome, and consists of a pair of nitrogenous bases that are held together by hydrogen bonds. The sequence of these pairs is “read” and used as instructions to build proteins. This happens in two separate processes, called transcription and translation. However, the relative rate at which a particular gene is transcribed is partially dependent upon epigenetic factors, or factors that affect the physical characteristics of an organism without changing the sequence of base pairs in the genome. Methylation is an example of one such epigenetic factor. Methylated genes are less accessible to the enzymes that enable transcription and translation to occur, and so the relative expression of these genes is reduced compared to that of nonmethylated genes.(2).
The researchers at UCLA studied the correlation between methylation and sexual orientation in 47 identical male twins. Since identical twins have identical sequences of DNA base pairs, individual variation is held to a minimum. Of the 47 pairs of twins, 37 contained one homosexual brother and one heterosexual brother, and ten pairs consisted of twins who were both homosexual (1).
The data collected from these twins proved difficult to analyze, mainly because of the large volume of data and the interrelatedness of epigenetic patterns among twins. In order to make sense of the data, researchers used a machine learning algorithm named FuzzyForest. FuzzyForest is capable of unsupervised learning, which means it is able to recognize patterns in the data and make predictions from them without human intervention. Using nine particular areas of the genome, the algorithm was able to correctly predict the sexual orientation of the participants about 70 percent of the time (1).
Researchers are now looking at testing the accuracy of this algorithm in the general male population. The results of this broader approach could bring about a more complete understanding of to what extent molecular and developmental biology can give rise to sexuality (1).
References:
- American Society of Human Genetics. (2015, October 8). Epigenetic algorithm accurately predicts male sexual orientation. ScienceDaily. Retrieved October 18, 2015 from sciencedaily.com/releases/2015/10/151008141634.htm
- Phillips, T. (2008) The role of methylation in gene expression. Nature Education 1(1):116