Other Traits

I just read an article about a South African teenage girl who was asked to take a gender test after winning an 800-meter race by a huge margin over the other runners. The article said that the gender testing was a very complex procedure. Why is it complex? Wouldn't a simple genetic test for a Y chromosome answer the question?

-A curious adult from Connecticut

September 15, 2009

It seems like it should be really simple! But it isn't. There is more to being a male than having an X and a Y chromosome. And more to being a female than having two X's.

This is because it isn't really the chromosomes that determine whether someone is a boy or a girl. Instead gender is determined by some of the genes on these chromosomes.

Some people end up with one of these genes that work differently. These people often have some male and some female attributes. Which is why gender testing can be so tricky.

Having qualities of both sexes is called intersexuality. That's just a fancy way of saying that there are some people that are like a female in some ways and a male in other ways. About 1% of people are like this " they don't fit the typical definition of male or female.

What I thought I'd do is go over what is looked at in gender testing and why. Then I'll go over some of the more common ways that someone can be intersex.

Gender testing

For the first part of the gender test, they will probably check for a Y chromosome. But as I said, this doesn't give you the whole story. So what else will they look for?

They will also check the levels of testosterone in the athlete's body. Both men and women make testosterone, but adult men usually have more than forty times the amount that women do!

Men make a lot more testosterone because it is important for early male development. Without it, no internal or external male body parts are formed. In adult men, testosterone is important for making normal sperm.

So if the female athlete has a huge excess of testosterone, then that will raise some red flags. The next part of the gender test will probably be to check to see whether the runner has female parts on the outside AND the inside. It is possible to look like a female on the outside, but not have the usual female parts (like ovaries, for example) on the inside.

So you can see that the results can be tricky to figure out. What if there is no Y, lots of testosterone and mostly female parts? Is the athlete female? What if the athlete has a Y chromosome but typical female levels of testosterone and is female on the outside?

As you can probably appreciate, making a human male or female is a really complex process. Lots of different genes have to all be set up just right to pull it off. What this means is that there are lots of ways to end up with something in between.

Common ways to become intersex

All embryos start out on a path to become females. This is the human default gender.

There is a gene on the Y chromosome that starts an embryo down the male path. This gene is called SRY. It is absolutely essential in becoming a human male. And in rare cases, it doesn't work properly.

Sometimes a person can end up with an SRY gene on an X chromosome. Now that person starts down the male path. This is called 46,XX testicular disorder of sex development. Around 1 in 20,000 people are thought to have this condition.

These XX people typically look male and are raised as such. But because the rest of the genes on the Y chromosome aren't present, these XX people tend to not develop fully male characteristics. And they need extra hormones when they reach puberty.

Sometimes a person can end up with a nonworking SRY gene on their Y chromosome. This person now stays on the female path. This is called Swyer syndrome. Around 1 in 30,000 people has this.

These people look female on the outside and have all of the usual female internal organs except ovaries. They are typically raised females and need hormone replacement therapy to reach puberty.

So should someone with Swyer syndrome be allowed to race against other women? What about the XX person who looks male? Should they race against women or men? This isn't easy, is it?

You may have noticed that both sets of people need hormones to mature. Another way to end up intersex is if something is different in a person's genes that make or interact with hormones.


Hormones are important during your development. If your body doesn't get the right hormones at the right times, things can end up a little different than expected. This can lead to a person being intersex.

One way this can happen is if you have a version of a gene called CYP21 that doesn't work well. This gene is important in the process of making cortisol. Cortisol is one of the hormones that respond to stress in your body.

People who have certain differences in CYP21 or other genes that affect the process of making cortisol have a condition called congenital adrenal hyperplasia (CAH). This can result in XX females that have male characteristics on the outside of their body. So how does this happen?

Well it all has to do with the process of making cortisol. There are many steps to go from a starting point to the final product, cortisol. Think of it like A has to turn into B, which is turned into C, which gets turned into D, which can then be made into cortisol.

People with different versions of CYP21 have a problem making something that is responsible for changing one of the steps into the next step. In other words, these people are missing the thing that makes B into C. If you never make C, then you don't make any cortisol either.

This also means that you are going to have a lot of B hanging around that doesn't get made into cortisol. Well, B can also be made into other things and one of those is testosterone.

This means that someone with CAH will usually have more testosterone than normal. When you are XX and have too much testosterone during development, it can cause you to have both male and female characteristics.

The opposite can happen too. You can have an X and a Y chromosome, but look completely female on the outside! This can happen when you have certain versions of the androgen receptor gene.

The androgen receptor is activated when testosterone binds to it. This triggers the development of male specific body parts. Some people have certain versions of the androgen receptor that are less responsive or unable to respond to testosterone at all. This is called androgen insensitivity syndrome (AIS).

Because people with AIS are unable to respond to testosterone, they can't develop the usual male body parts. So people with AIS are generally XY with female characteristics. They usually do not have female parts on the inside. People with AIS might not even know that they have a Y chromosome!

Because of these possibilities (and more), the gender test must look at many different things. Each part is sort of like pieces of a puzzle. Once the judging committee has all of the pieces, they will have to make a tough decision! 

Jamie Conklin

There is more to being a male than having a Y chromosome.

Making babies is complicated and sometimes things don't go as planned.