In 2011, the famous singer Lady Gaga sang her song “Born this way”; The song quickly became an anthem at gay parades. Indeed, over the course of two decades, researchers have been able to discover ample evidence that homosexuality is not a choice, but rather is deeply embedded in an individual's biology, determined by genes. However, the locations of the 'gay genes', as they are called, remain a mystery.
A new study may help us understand this. The study was conducted on male twins and was presented at the American Society of Human Genetics (ASHG) annual meeting in Baltimore, Maryland.
This study found that some epigenetics—chemical changes in the human genome that alter the nature of gene activity without altering its chemical sequence—may affect sexual orientation.
Researchers thought they had come very close to the "homosexuality gene" in 1993 when a team led by Dean Hamer published a scientific article on the presence of one or more homosexuality genes on the X chromosome's long arm at position 28 (Xq28).
This discovery became the headline in many international newspapers, but some reviewing scientific groups were unable to obtain the same results of that study, and were unable to find the genes that were published in Hammer's study, and even one of the scientific teams that acknowledged what Hammer found in his study, tried to The following year, the study searched for "Gene Hammer" in a larger sample of people, more than ten times the number of Dean Hammer's group, but did not obtain the same results.
In addition, studies of twins indicated that we are unlikely to attribute the entire cause of homosexuality to genetic sequences.
As in identical male twins, if one of the twins is gay, the probability of the other being gay is only between 20% and 50%, despite having the same genome, and in the case of heterosexual twins, the probability is 13%. These studies show that there is a genetic effect on sexual orientation, but not to the extent that it justifies looking at it as a purely genetic phenomenon. Therefore, it was suggested that changes in creation are among the causes of homosexuality, whether that makes it the only cause of homosexuality, or makes it an additional reason for it.
During human development, its chromosomes undergo chemical changes that do not affect the sequence of its nucleotides, but turn genes on and off.
The best example of this is methylation, the addition of a CH3 methyl group to specific gene regions.
These epigenetic signs remain influential in genes throughout life, but most of them do not pass on to eggs or sperm when they are formed, as genes begin in those gametes as a white page without additions or signs. However, some recent studies have shown that some of these signs persist and remain for the next generation.
In a 2012 paper, William Rice suggested that these inherited meta-marks may be the cause of homosexuality when passed from father to daughter, or from mother to son.
Scientists have argued that inherited traits may affect a fetus's sensitivity to testosterone, which could either "masculine" female brains (make them more masculine) or "feminize" male brains (make them more feminine), leading to same-sex attraction.
Such ideas inspired Tuck Ngun to study the patterns of methyl groups in 140,000 regions of DNA belonging to 37 pairs of identical male twins, one of which was gay and one heterosexual, and of another 10 pairs of identical male twins, all of whom were gay.
After iterating the analyzes several times, and with the help of a newly developed computer algorithm, the team of researchers identified five regions of the genome to which adding a methyl group is closely associated with homosexuality.
One of these genes was important for nerve conduction, while another was involved in immune function.
To test the importance of these five regions, the scientists separated identical twins in which one member was gay into two groups.
They then examined the relationships between epigenetic markers and sexual behavior in one group.
Then, how these results predicted sexual orientation was tested on the second group.
The scientists managed to reach an accuracy rate of 70 percent.
In a 2012 paper, William Rice suggested that these epigenetic markers may be the cause of homosexuality when passed from father to daughter, or from mother to son.
The scientists state that inherited traits may affect the fetus's sensitivity to testosterone, which may "masculine" female brains (make them more masculine) or "feminize" male brains (make them more feminine), leading to same-sex attraction.
Ideas such as these inspired Tuck Ngun to study the patterns of methyl groups in 140,000 regions of DNA in 37 pairs of identical male twins in which one was gay and one heterosexual, and studied them in 10 other pairs of identical male twins in which both were The twins are gay.
After iterating the analyzes several times, and with the help of a newly developed computer algorithm, the team of researchers identified five regions of the genome in which methylation is closely associated with homosexuality.
One of these genes was essential for nerve conduction, while another was involved in immune function.
To test the importance of these five regions, the scientists separated identical twins in which one partner was gay into two groups.
Then they examined the relationships between epigenetic signs and sexual orientation in one group.
Then, they tested the effectiveness of the results in predicting sexual orientation in the second group.
The predictions were 100% accurate
70%.
But scientists still insist that these predictions apply only to the sample of twins who were tested, and not to the rest of the population.
It is unclear why there are different methyl group patterns in identical twins.
And if Rice's hypothesis is correct, then the epigenetic signs from the mother were erased in one of the two sons without the other.
Or maybe neither of them inherited those marks, but one of them acquired them in his mother's womb.
In a previous study, Ngon and colleagues reported evidence that methylation may be determined by small changes in the environment of the fetus as it develops and develops its organs, such as the location of the fetus in the womb and the amount of blood it receives from the mother.
“These simple effects are the key,” says psychologist J. Michael Bailey of Northwestern State University in Evanston, Illinois. Identical twins in which one partner is gay is the best way to study this.” He and Rice insist that this study needs to be repeated in a larger sample of people in order for its results to become clearer and more certain.
The study would be even more convincing if those areas that show epigenetic signs were linked to broad changes dependent on their sensitivity to testosterone in the womb.
Scientists stress that these results should not be used in tests to determine homosexuality or not, or in the search for what is misleadingly called a “treatment” for that condition.
But scientists are not worried about this, as it is known that we will not have the ability to manipulate sexual orientation in the near future.
According to a 2008 study, there is ample evidence to support that sexual orientation is influenced by genetic factors.
Homosexuality impairs reproductive success, and therefore its presence in populations at relatively high rates is a mystery. However, the results of this study showed that the genes that predispose a person to homosexuality are in fact beneficial to heterosexuals, and this benefit enhances their mating success.
According to another 2009 study, the fertility of females with same-sex maternal relatives is high, which increases their reproductive success, and thus the "gay genes" are more likely to be inherited by some individuals in later generations of their offspring.
There is research that contests the idea that homosexual behavior in animals impairs their reproductive success, and there are many theories that say that it is adaptive behavior, and these theories differ according to their species.
According to some research, homosexual tendencies are influenced by the hormonal environment in which the fetus develops.
Hormonal factors influence brain structure and other features.
The activity of testosterone is what makes the fetal brain grow into a male brain, and the lack of effect of this hormone is what makes it grow into a female brain.
According to research conducted in 2010, this is how gender identity and sexual orientation are determined, as it is programmed into the structure of the fetal brain while it is still in the womb.
In addition, brain research has shown differences between homosexuals and heterosexuals in terms of the size of certain brain nuclei.
Bone length is another characteristic affected by sex hormones that is thought to be related to homosexuality. The bones of the arms, hands and legs are shorter in gay men.
But it is not clear: Do these traits cause or express homosexuality? (That is, the cause-and-effect relationship is not clear).
Margins:
Epigentics is the primary science used to explain sexual behaviors and orientations in this study. It studies changes in the 'activity' of a gene, not its structure; In the sense that every cell in your body has the same genes, but each gene in each cell is expressed in a distinct way, so your liver cells do not release nails, and your skin cells do not produce insulin. It is the study of changes that cause genes to 'turn on' and 'off' without manipulating their sequence.
Heterosexual: Someone who is attracted to the opposite sex.
Homosexual: Someone who is attracted to people of the same sex.
the reviewer1- Zietsch، Brendan P. (2008). “Genetic factors predisposing to homosexuality may increase mating success in heterosexuals”. Evolution & Human Behavior 29 (6): 424–433.
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4- Kendler، Kenneth S. (2000). “Sexual Orientation in a U.S. National Sample of Twin and Nontwin Sibling Pairs”. American Journal of Psychiatry 157 (11): 1843–1846.
5-Rahman، Qazi (2005). “The neurodevelopment of human sexual orientation”. Neuroscience and Biobehavioral Reviews 29: 1057–1066.
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