Guest Blog by Joni Bosch

Many times I have heard people dismiss the idea that sexual orientation is not a choice by saying “there is no gay gene.”   Well, not so fast, since there is probably no straight gene either. The statement itself actually displays a serious lack of understanding of genetics.

I currently work in the genetics clinic doing follow up care for patients with known genetic diagnoses. I am not a geneticist nor am I a genetic counselor. But I would like to try to explain a little of the complexity of genetics. I hope that understanding a little more about the complexity of it all might help when dealing with people who think they have a trump card in their “no gay gene” declaration.

You probably remember something about Gregor Mendel and his peas. He helped clarify one type of inheritance—recessive and dominant. If you inherit a dominant trait from one or both parents, you will express that dominant trait—Type A blood, for example. To express a recessive trait you have to get the recessive gene from both parents, type O blood, for example. A parent might have two A genes or one A gene and one O gene. What each child is likely to be is related to whether the parent has one or two A genes. This is probably the most obvious type of inheritance.

The problem is that most of life just is not that simple. There appear to be around 150 genes associated with height. If you have “Tall” genes but are malnourished as a child, those “Tall” genes probably won’t do you much good. So we know that more than one gene can influence aspects of who we are, and that genes interact with our environment.

Epigenetics looks at how our life experience (including prenatal life) can affect our genes without actually changing our DNA. I used to think my DNA was like a hallway with my genes behind doors that were all open and usable. However, some of our DNA “doors” are locked after we reach certain developmental stages and that DNA is no longer needed, for instance, some types of hemoglobin that we only need as babies in our mothers’ wombs. Some of those doors have to be open all the time in order for cells to do their work. Still others of those doors can be opened or shut, locked or unlocked, by exposures in our environments. Too much or too little food may open or shut genetic doors that can affect the developing baby and even that baby’s own children some day, in terms of problems like obesity and diabetes.

In fact, there are relatively few genes in which a variation or mutation always causes a specific trait or problem. The genes for breast cancer and early onset Alzheimer’s disease seems to cause problems for about 80% of the carriers, while the other 20% do OK. Penetration is the term used to describe whether a person with a known genetic variant actually shows signs of having that phenotype or problem. Expressivity is another genetic idea.

Pretend there are Hairy genes and Hairless genes. Penetration will determine how likely it is that a person will be Hairy as opposed to Hairless if they have the Hairy gene. If the Hairy gene is fully penetrant, everybody with the Hairy gene will be Hairy. If it is not fully penetrant, some people with the Hairy gene might not be Hairy at all. They might look Hairless but have Hairy children. Expressivity tells us whether those who have the Hairy gene will be very hairy all over, or hairy in spots, or have just a little Hairiness. So having a gene for something does not tell us for certain just exactly how having it will affect us.

A more real example is Neurofibromatosis or NF. A parent might have NF but only have some freckles in their armpits and some café au lait spots on their skin. However, they could have a child with an optic tumor and a lot of neurofibromas. Imprinting is another interesting part of genetics.

Some genes work only if they came from the mom or only if they came from the dad. If you can only use Dad’s gene and it has a problem, you can’t use Mom’s gene even if it is perfectly good. Prader Willi syndrome and Angelman syndrome are examples of genetic conditions that are caused by problems with imprinted genes.

It is also becoming clear that our biome, all the germs and other critters that live in and on our bodies (and who outnumber us) also play a role in how our bodies work—and they have genes of their own. Even if we can identify a gene that causes a problem or trait, identifying everything that might turn it on or off can be a problem. Some regulatory functions of a gene may be way up or down the chromosome from the gene itself. So knowing that a gene is present and that all the DNA is in the right order does not guarantee there is no imprinting problem or other regulatory problem further away.

So, does sexual orientation have a genetic basis, and how would we know? The answer is yes, sexual orientation, both gay and straight, does seem to have a genetic basis, although at this time there is no gay or straight gene that guarantees that its owner will be one or the other. Further complicating that picture is that whatever is going on may not work the same in males and females. We have been able to identify some physiological markers, but we are probably dealing with a combination of susceptibility genes interacting with environmental influences.

When I say “susceptibility gene”, think “genetics loads the gun but environment pulls the trigger.” A susceptibility gene seems to increase the chance that a trait will be expressed that is different than the typical trait associated with that gene. This gets really complex. For instance, there are a lot of genes that appear to be susceptibility genes for autism spectrum disorder. There are also a lot of things that are not genetic that seem to correlate with autism spectrum disorder, such as maternal stress during pregnancy, parental age and father being an engineer. Another example of complexity is an eye disease which requires mutations to have occurred on two entirely different chromosomes to have the disease. Again, you see how complex it can be to try to figure out the “cause” of anything.

At this time it seems most likely that some people are more susceptible to alterations in prenatal sex hormones, especially testosterone, than others. Our genes interacting with our prenatal environment leads us to have brains and bodies that are sexually dimorphic—that is typically developing male and female brains and bodies show differences both in structure and in how they work

Research studies looking at physiological differences between those who are gay and those who are straight generally find that gay men have differences that pull them closer to straight women and that gay women have differences that pull them closer to straight men. (And as I type this, I realize that society seems to put a premium on straight men but that is a different story.)

There is also some evidence that men with several older brothers are more likely to be gay. It has been proposed that a mother may have some type of immune reaction to male hormones, but at this time there is no proof of this. On the one hand, we are all a combination of our genes interacting with our environment and our lived experiences.

In my opinion, there is plenty of evidence indicating that sexual orientation is not a choice, or at least that there are significant genetic and biological influences tilting us one way or the other.

Of course, any one of us could enact the most telling test of all..  Ask a gay person if they chose to be gay or whether it was instinctual.  I know I never made a choice to be straight.

More to the point, who cares? It seems that debating whether or not sexual orientation is innate or chosen is rather like debating whether blue eyes or red hair is bad simply because they are not typical of the majority of the human population. After all blue eyed people could simply wear brown colored contacts in order to fit in and red heads could dye their hair. Atypical should not be viewed as bad. The whole point of genetics and sexual reproduction is variability. Variability gives us strength and helps us survive as a species. It is something we should celebrate and cherish.  

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