The X’s and Y’s of Sex: What Makes a Boy or a Girl

Infant feet-01Remember high school biology? You were taught that humans had forty-six chromosomes. There were two each of twenty-two pairs, and then there were your sex chromosomes, the Xs and Ys. If you had two X chromosomes (XX), you were a girl. An X and a Y (XY) made you a boy.

It’s not actually that simple. That is the most common arrangement, but there are many variations. When you have a variation on any other chromosome, it causes physical issues that are unfortunate and sometimes deadly. If you have three number twenty-one chromosomes you have Down’s syndrome, and your life will be different.

We don’t ever blame the child, right? Nobody asked them if they wanted the usual forty-six chromosomes or if they would mind having an extra. It’s not their fault.

When the extra or missing chromosomes are the Xs or Ys, suddenly we involve social judgment and religion. Why? I can only assume that we are all so uncomfortable with sexuality that we would rather judge than understand.

You’re reading the wrong blog if you wanted to get away with that.

Variations

One in 840 male births are an XYY. We used to think that this made the men more violent because the tests were all done on men in prisons. Once we started testing men who were not in prison, it turned out that there weren’t actually many differences. Most are completely normal. There is a mild tendency toward tallness, poor fine motor control, weakness, and some speech and language issues. Most of these guys never know they aren’t the typical XY.

One in 500 males have XXY, or Klinefelter’s disease. These kids do have some physical issues, such as a tendency toward long limbs, smaller genitals, and slightly less intelligence than they would have had without that extra chromosome.

When you get into larger numbers of chromosomes, you see more problems. XXYY and XXXY kids tend to need testosterone replacement. XXXY and XXXXY kids tend to be short with small genitals, mental defciency, and elbow issues.

Without any Y chromosome, we get girl babies. XXX girls are usually tall and sometimes uncoordinated. Rather like the XYY males, most won’t ever know they have it. Girls with as many as five X chromosomes have been found. The more X chromosomes they have, the more problems: they tend to become shorter, with mental defciency and behavior issues.

About one in 2,000 live births are XO girls who are missing one X or Y chromosome. They have Turner’s syndrome. They have lymphedema (fluid swelling under the skin) before they are born and frequently have extra skin at the neck. They tend to be short, with wide chests and gonadal dysgenesis (sex organs that do not develop normally).

To add to all these variants, we have mosaics: two fertilized eggs fuse so that the resultant person has half a body with the typical XX or XY and half a body with a variation.

Variations with the Usual Chromosome Count

There are also variations that occur with the typical complement of chromosomes.

Girls with testicular feminization have 46XY. Their chromosomes say “boy,” but their bodies are insensitive to testosterone. They grow up as girls and don’t realize there is a problem until adolescence, when fertility issues arise.

Congenital Adrenal Hyperplasia (CAH) will give you a baby that has been virilized. On a girl, the clitoris will be enlarged, and the labia can become fused. It is difficult to tell when the baby is born if it is a boy or a girl until the chromosomes come back. Since the first question everyone asks is “Is it a boy or a girl?” this can be very traumatic to the families involved.

Adrenocortical tumors can also be virilizing, giving the child more masculine traits than they otherwise would have had.

Enough? There are many more. Biology is not as simple as they taught you in grade school, and throwing judgment and religion at it does not change it or help in any way. Ignorance is ugly.

The gender issues and sexual orientation parts of this blog got really long, so…

Come back next week please!

The Blogger's Pit Stop

3 thoughts on “The X’s and Y’s of Sex: What Makes a Boy or a Girl

  1. Looking forward to your continuation on this post when you further discuss gender. Currently working on a book that discusses this very topic and interested to hear your own thoughts on it. Sincerely, Cheryl B. Evans (Author of I Promised Not to Tell: Raising a transgender child).

    Liked by 1 person

    • This post is actually a few weeks old, so the gender one is already there. I wish I had better science for gender, but it’s just not out there yet. One thing that intrigues me: when a child is born with ambiguous genitalia we chose a sex for them based on their chromosomes. Those children are more likely to be transgender, and we have no idea why.
      Please let me know when your book is out, I would love to read it!
      Good luck!

      Like

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