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Girl with a Y chromosome July 4, 2009

Posted by Geekgirl in genetics.

A little quiz. If you have two X chromosomes you….. a girl, right? If you have one X chromosome and one Y chromsome, you are a boy, right?

Not always. Just mostly. In science, there are few absolutes.

In April 2009, New Scientist reported on a girl born with a Y chromosome. During pregnancy, the mother had a routine amniocentesis to check for Down’s Syndrome. As part of the test, the gender is learned. But instead of welcoming a little boy into the world, their child was born a girl. How can this be?

Scientists in Switzerland and Luxembourg belief that hinks the patient’s normalcy is due to mutations in a poorly understood gene on chromosome 17 called CBX2. Please note, chromosome 17 is what is refered to as an autosomal chromsome. This means that both boys and girls will have this chromosome. The only difference, chromosome wise, between girls and boys is the Y chromosome.

The protein that this gene codes for is involved in the development of male genitalia. Typically, if a girl has a Y chromosome, she will have a poorly developed uterus and ovaries. As far as doctors are able to tell, this little girl has a normal uterus and ovaries. Since she is currently around the age of 8, only time will tell if she will be fertile, straight, gay or transgendered.
New Scientist link to article

American Society of Human Genetics. link to scientific abstract

The American Journal of Human Genetics, Volume 84, Issue 5, 658-663, 09 April 2009

Ovaries and Female Phenotype in a Girl with 46,XY Karyotype and Mutations in the CBX2 Gene

Anna Biason-Lauber1,2,,,Daniel Konrad1,2,Monika Meyer1,Carine deBeaufort3andEugen J. Schoenle1,2

Corresponding author


A girl with a prenatal 46,XY karyotype was born with a completely normal female phenotype, including uterus and histologically normal ovaries. In mice with a similar phenotype, the ablation of M33, an ortholog of Drosophila Polycomb, causes male-to-female sex reversal. The analysis of the human homolog of M33, Chromobox homolog 2 (CBX2), in this girl revealed loss-of-function mutations that allowed us, by placing CBX2 upstream of SRY, to add an additional component to the still incomplete cascade of human sex development.



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