December 12, 2012
Epigenetics Reveal Biological Information On Homosexuality
[ Watch the Video: Researchers Say They Have Found Genetic Switches for Homosexuality ]
Connie K. Ho for redOrbit.com — Your Universe Online
To begin, epigenetics looks at how gene expression is managed by temporary switches, known as epi-marks. In the report, recently published online in The Quarterly Review of Biology, the authors discussed how sex-specific epi-marks generally do not transmit between generations and are considered “erased.” Homosexuality can result when these marks are not “erased” and are passed on from father to daughter or mother to son.
"Transmission of sexually antagonistic epi-marks between generations is the most plausible evolutionary mechanism of the phenomenon of human homosexuality," explained the study's co-author Sergey Gavrilets, who serves as the NIMBioS' associate director for scientific activities and professor at the University of Tennessee-Knoxville, in a prepared statement.
The researchers explain how homosexuality is common for men and women in various cultures despite knowledge of evolutionary methods. Past studies have looked at how homosexuality is passed through family members, but no gene related to homosexuality has been found. The current study by the researchers from the Working Group on Intragenomic Conflict at NIMBioS produced a biological and mathematical model based on evolutionary theory and new information on gene express and androgen-dependent sexual development.
In particular, epi-marks give an extra set of information on the expression of genes. Genes have instruction, while epi-marks manage how the how gene instructions are carried out during gene development. For every generation, there is a new set of epi-marks; however, studies have also shown that epi-marks may be passed between generations and can cause similarity among relatives.
"There is compelling evidence that epi-marks contribute to both the similarity and dissimilarity of family members, and can therefore feasibly contribute to the observed familial inheritance of homosexuality and its low concordance between [identical] twins," the study´s co-author William Rice, a professor at the University of California, Santa Barbara, told U.S. News.
In addition, sex specific epi-marks found in early fetal development help protect each sex from having natural variation in testosterone that occurs later in fetal development. For example, sex specific epi-marks will prevent girl fetuses from becoming too masculine while preventing male fetuses from becoming too feminine. Though, when epi-marks are transmitted from one generation to the next, from father to daughter or mother to son they show reversed effects. In this regard, some traits in sons become feminized while other traits in daughters become more masculine.
"Most mainstream biologists have shied away from studying it because of the social stigma," continued Rice in the article by U.S. News. "It's been swept under the rug, people are still stuck on this idea that it's unnatural. Well there are many examples of homosexuality in nature, it's very common."
Furthermore, the mathematical modeling of the genes shows that the epi-marks can be passed on the population as a way to boost the fitness of the parent but decreasing fitness in offspring.
"These epi-marks protect fathers and mothers from excess or underexposure to testosterone – when they carry over to opposite-sex offspring, it can cause the masculinization of females or the feminization of males," commented Rice in the U.S. News article.
Overall, the study helps explain the various underling factors related to homosexuality.
"We've found a story that looks really good," concluded Rice in the U.S. News article. "There's more verification needed, but we point out how we can easily do epigenetic profiles genome-wide. We predict where the epi-marks occur, we just need other studies to look at it empirically. This can be tested and proven within six months. It's easy to test. If it's a bad idea, we can throw it away in short order."