The Genetics of Sexual Development

The Genetics of Sexual Development

by Dr. Hsien-Hsien Lei
Posted May 25, 2007 in DNA and Disease

All parents wonder whether their unborn child will be a boy or girl. Some choose to find out early with the help of gender prediction DNA tests or ultrasound. But for one in 4,500 births, babies are born with a “disorder of sexual development” (DSD)* in which their genitals are considered to be “intersex.” Five sex-assignment surgeries are performed in US hospitals each day.

Dr. Eric Vilain of UC Irvine is studying the genetics of sexual development. His lab has found 50 new gene candidates on multiple mice chromosomes that may be involved in differential sex expression. This is in addition to:

  • SRY male-determining gene on the Y chromosome
  • DAX1 female-determining gene on the X chromsome
  • WNT4 female-determining gene on chromosome 1

middlesexCoincidentally, I am about to begin reading Middlesex, a fictional account of a hermaphrodite, by Jeffrey Eugenides. I wonder how my understanding of the book will be filtered through the knowledge of multiple genes affecting gender determination.

Have you read Middlesex? What did you think?

*Dr. Vilain and the Intersex Society of North America are working to have replace “hermaphrodite,” male or female “pseudohermaphrodite,” and “intersex” with “disorder of sexual development.”

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Comment by alicia Subscribed to comments via email

OK, help me out here. These “chromosomes that may be involved in differential sex expression,” along with the other three you listed – are these what help doctors determine if the sexual assignment surgeries should “assign” a baby as male or female?

I’m assuming if the surgery isn’t done when the person is a baby, they can make their own decision when they’re older and realize their situation.

Comment by Hsien

That’s a good question, Alicia. According to the Scientific American article I linked to above, a lot of times the decisions have less to do with the patient’s genetic make-up than with the doctors’ emotions. Dr. Vilain says,

What really matters is what people feel they are in terms of gender, not what their family or doctors think they should be.

You’re very insightful!

Comment by alicia Subscribed to comments via email

Thanks for the clarification! Your post reminded me of an episode of Grey’s Anatomy (that show actually teaches a little something, haha), but I didn’t mention it for two reasons. One, a London friend of mine (*cough* a singer whose song actually appeared on one of the GA episodes *cough*) told me England was behind in the episodes, and two, I thought I’d look foolish, lol.

Anyway, Addison, the resident obgyn surgeon, refuses to perform a sexual assignment surgery on a teenage “girl” who is in the hospital for some other reason. Addison finds out the girl actually has testes near her ovaries, the parents freak, don’t want her to tell their daughter, and actually ask if Addison will remove them when she’s performing the other surgery. Addison refuses and there’s this whole theme about morals and ethics and whatnot going on.

So, your post got me to thinking…if a doctor wouldn’t do it to a girl who was old enough to make her own decision, would one do it to a baby?

Too, it turned out the girl was relieved to find out she could be a boy if she wanted to – and opted to.

(Comments wont nest below this level)
Comment by Hsien

Interesting!! I found the episode summary at Television Without Pity in case anyone wants to read more. Thanks for sharing, Alicia!

Comment by Hsien

For others who are interested. An old post of mine:

In men, the SRY (sex-determining region Y) gene on the Y chromosome determines the development of male characteristics. The corresponding gene in women may be the R-spondin1 (RSPO1) gene. People with the XX genotype who would normally be women become men if they have a non-functional RSPO1 gene. The gene was discovered in a family of four sons who all had two X chromosomes, no SRY gene, and mutations in the RSPO1 gene.

Comment by laura Subscribed to comments via email


great book. you have been reading some great stuff lately.

I liked it!

Of course, I don’t have your background in genetics. But it made me look at people a little differently, and think about the secrets that we are hiding.

Comment by Hsien

Me? Secrets? Just check my Facebook. ;)


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