Questions about Homosexuality

The lab is also testing an intriguing theory involving imprinted genes. Normally, we have two copies of every gene, one from each parent, and both copies work. They're identical, so it doesn't matter which copy comes from which parent. But with imprinted genes, that does matter. Although both copies are physically there, one copy - either from the mom or the dad - is blocked from working. Think of an airplane with an engine on each wing, except one of the engines is shut down. A recent Duke University study suggests humans have hundreds of imprinted genes, including one on the X chromosome that previous research has tied to sexual orientation.

With imprinted genes, there is no backup engine. So if there's something atypical in the copy from mom, the copy from dad cannot be turned on. The UCLA lab is now collecting DNA from identical twins in which one twin is straight and the other is gay. Because the twins begin as genetic clones, if a gene is imprinted in one twin, it will be in the other twin as well. Normally, as the fetuses are developing, each time a cell divides, the DNA separates and makes a copy of itself, replicating all kinds of genetic information. It's a complicated but incredibly accurate process. But the coding to keep the backup engine shut down on an imprinted gene is less accurate.

So how might imprinted genes help explain why one identical twin would be straight and the other gay? Say there's an imprinted gene for attraction to females, and there's something atypical in the copy the twin brothers get from mom. As all that replicating is going on, the imprinting (to keep the copy from dad shut down) proceeds as expected in one twin, and he ends up gay. But somehow with his brother, the coding for the imprinting is lost, and rather than remain shut down, the fuel flows to fire up the backup engine from dad. And that twin turns out to be straight.

One of the most compelling aspects of the nature vs. nurture argument is provided by studies of identical twins (exact genetic copies of each other).

[b]Bailey and Pillard (1991): occurrence of homosexuality among brothers[/b] * 52% of identical (monozygotic) twins of homosexual men were likewise homosexual * 22% of fraternal (dizygotic) twins were likewise homosexual * 11% of adoptive brothers of homosexual men were likewise homosexual

and

[b]Bailey and Pillard (1993): occurrence of homosexuality among sisters[/b] * 48% of identical (monozygotic) twins of homosexual women were likewise homosexual (lesbian) * 16% of fraternal (dizygotic) twins were likewise homosexual * 6% of adoptive sisters of homosexual women were likewise homosexual

http://www.worldpolicy.org/globalrights/sexorient/twins.html

If nurture (how someone is brought up, who they are exposed to, what they see, what choices they make) was the main element, there should be far more correllation between identical and fraternal twins than there is.

http://www.boston.com/news/globe/magazine/articles/2005/08/14/what_makes_people_gay/

Well, as I said before, default mode for most kids is assuming they're heterosexual. That's what they see everywhere around them, in books, in movies -- heterosexual couples. Little girls dream about getting married, going to the ball with the prince, that kind of thing. If that little girl grows up and thinks both "gosh, Katrina is so beautiful" and gets a little warm and fuzzy inside, she can just put that under the category of "friendship"; if she thinks "gosh, Kurt is so handsome", she goes ahead and assumes she has a crush on him.

So the default mode is heterosexuality.

For people who are in fact homosexual, they may realize sooner or later that it's not just that the person is beautiful or handsome, but that he or she has sexual feelings towards that person.

Then the process of dealing with it begins. Deny it? Act on it?

For a lot of people, the process begins with denial, and stops when it simply can't be denied any more.

If the tendancy to homosexuality is genetically passed on then it will be part of the DNA that comes from the father/mother. Half of the DNA comes from each parent. Each of us carries chromosomes from each of our parents and pass on one of those for each trait. For instance you might have recieved a chromosome for blue eyes from one parent and brown eyes from another parent. You don't have blue/brown eyes. You demonstrate one eye color (brown in this case because it is dominate) but you are capable of passing on the blue eye color gene to your children. If a homosexual passes on a genetic tendency then it will be passed on approximately 50% of the time (unless he has recieved it from both of his parents and then he will pass it one 100% of the time).

The 50% (approx) figure is significant in two different ways. First, it's like having a son or a daughter. The male will pass on the X chromosome half the time (resulting in a daughter) and the Y chromosome the other half (resulting in a son). Monozygotic twins have identical DNA because they start out as one egg/sperm. You would expect a genetic tendency to equal approx 50% because the gene associated with it would be passed on half of the time. I'll get to the other way it's significant in a minute.

Approx 20% of dizygotic twins were likewise homosexual. This is as expected because there are two sperm and two eggs involved. If one parent in passing on a genetic tendency to homosexuality then the chances of both sperm/egg pairs recieving the gene are half of the case above.

The 6% to 11% of adoptive siblings being homosexual might represent random chance or it might reflect an environmental influence.

Now, back to the 50% and the 20%. Consider that twins being raised in the same environment would have the same likelihood of both being gay. If there was no genetic influence then it wouldn't matter if the twins were identical (monozygotic) or fraternal (dizygotic). From before, in the absence of a genetic influence, there would be no difference between the rates of homosexuals in any children being raised in the same environment. The fact that the monozygotic twins were homosexual 50% of the time, the dizygotic twins were homosexual approx 20% of the time and the adopted (non-genetically linked) siblings were homosexual only 6-11% demonstrates a strong likelihood that the environment is not the primary influence.

This is lots of numbers and I'll be happy to break them out further if it would help clarify things.

Oh man, I'm bursting to say something, but first I wanted to read through the entire thread. I think this thread could really be positive.

I absolutely loved this, Soz, because it is so 'typical' an experience, especially in the West, and I couldn't have said it better myself:

Well, as I said before, default mode for most kids is assuming they're heterosexual. That's what they see everywhere around them, in books, in movies -- heterosexual couples. Little girls dream about getting married, going to the ball with the prince, that kind of thing. If that little girl grows up and thinks both "gosh, Katrina is so beautiful" and gets a little warm and fuzzy inside, she can just put that under the category of "friendship"; if she thinks "gosh, Kurt is so handsome", she goes ahead and assumes she has a crush on him.

So the default mode is heterosexuality.

For people who are in fact homosexual, they may realize sooner or later that it's not just that the person is beautiful or handsome, but that he or she has sexual feelings towards that person.

Then the process of dealing with it begins. Deny it? Act on it?

For a lot of people, the process begins with denial, and stops when it simply can't be denied any more.

So far, I really like the Kinsey scale, because it at least acknowledges that people are not either straight or gay!, but we are actually a continuum of expressions and sexual orientations.

I am one of those people who falls between a 3-4, who 'goes either way', or call me a bisexual if you want. lol. I could tell many a-story, like so many other people out there, and I am open to sharing anything that may help to spread some knowledge about.

The culture we grow up in tells us to choose: gay or straight (but of course we'd rather prefer if you are straight). Such tight little boxes that can cause so much pain.

I am interested in seeing more numbers and studies, so thanks. J.B. , Soz, and others, i look forward to seeing more posts like that. I do believe there is a genetic factor involved, but am not set .

Regardless of why or how someone is gay(or any variation beyond straight); the important thing in my eyes is that EVERYONE is given the space to be who they are. Really, that is what it is all about.