Scientists tie homosexuality to chemical markers that accompany DNA.

[DetlefK]

http://throb.gizmodo.com/report-dna-markers-accurately-predict-male-homosexuali-1735515589
http://www.nature.com/news/epigenetic-tags-linked-to-homosexuality-in-men-1.18530

First:
DNA is not a blueprint. It's a step-by-step "How-to"-manual. In a given situation, the body reacts by activating the appropriate "step", a gene, from the DNA. A copy of the instructions is made in the form of a strand of m-RNA. And the instructions on the m-RNA are then put to work with the aid of r-RNA and t-RNA, constructing a protein, a "chemical machine", that is tailor-made for taking care of this specific situation.

That's not the whole story: There are chemical markers attached to the DNA. They influence how the genes get expressed.

Scientists compared 37 pairs of identical twins where one was gay and one was not, and 10 pairs of identical twins where both were gay.

To search for factors that could mediate a link between environment and genes, geneticist Eric Vilain at the University of California, Los Angeles (UCLA), and his colleagues looked at epigenetic markers — chemical changes to DNA that affect how genes are expressed, but not the information they contain. These 'epi-marks' can be inherited, but can also be altered by environmental factors such as smoking, and are not always shared by identical twins.

The researchers collected DNA samples in saliva from 37 pairs of identical twins in which only one twin was gay, and 10 pairs in which both were gay. By scanning the twins’ epigenomes, the researchers found five epi-marks that were more common among the gay men than in their genetically identical straight brothers. An algorithm they developed based on the five epi-marks could correctly predict the sexual orientation of men in the study 67% of the time.

...

Vilain is not surprised to find that epigenetics is associated with sexual orientation, although he says it is too early to try to directly link the epi-marks to any particular environmental exposure or the expression of a specific gene.

...

Vilain acknowledges limitations of the study — for instance, epigenetic markers differ between tissues in the body, and those in the brain are probably most relevant to sexual orientation.

...

“We already know there is no 'gay gene',” says William Rice, an evolutionary geneticist at the University of California, Santa Barbara. If there were, he says, it would have turned up in one of the massive studies that scan the whole genome for variants shared between gay people.



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IMO, the fact that the chemical markers can change might also explain the phenomenon of "late-blooming lesbians", heterosexual women that turn homosexual at a certain age.

And it would explain why there are different degrees of bisexuality between heterosexual and homosexual.

[safeinOhio]

1. Nature vs nurture.

When a trait is found among all cultures across all times, it's nature not nurture.

[madokie]

2. I have a real dear friend

who was gay from the day he was born onward. He never played with us guys, rather he spent his time with the girls. Me it was toy trucks and tools, him it was dolls and makeup. I love him like a brother but he is more like a sister. He had no say in any of this, he was simply born a girl in a boy body. Simple as that.

And it pisses me off to no end when I see or hear of anyone putting down or giving a hard time to a gay person. I used to have to fight to protect him when we were kids and Fight I did.

[Ms. Toad]

4. Transgender is not synonymous with gay.

Spending time with girls and playing with dolls and make-up is not synonymous with either. Being born a girl in a boy body is a colloquial expression for being transgender (but some transgender individuals reject that description).

You haven't mentioned anything about sexual attraction (which is what being gay is about).

Trangender individuals can have any sexual orientation.
Gay individuals can be either trans- or cis-gender.

[Bohunk68]

3. The 5 September 2015 issue of Science News

is dedicated to this item. On page 18, the article starts about how loops and enhancers work. A couple of months ago, met a student at our local SUNY campus who was from Brazil and studying epigenetics. In light of this post, it is interesting to note that he was also gay. I don't know if that had a bearing in his decision for field of study.