Baldness Doesn’t Come from Your Dad

I once saw a commercial for a rogaine-like product that helps bald men recultivate their bald patches. The man in the commercial walks down a hallway practically wallpapered with family photos as he describes the annoyances of baldness. He gets to a picture of his father and sassily says, “Thanks, dad.”

I completely understand why a man would assume he gets the baldness gene from his father, but it’s just not true. Men, if you go bald, the only person you can blame is your mother (but please don’t blame her anyway).

(For the record, I don’t like the idea of the man in the rogaine commercial saying, “Thanks, mom,” and rolling his eyes. It might be correct, but it’s still not cool.)

The gene for baldness or none-baldness is on the X chromosome. You have probably heard of the X and Y chromosomes, also called sex chromosomes because, yes, they determine the sex of the person.

You get half your chromosomes from your mother’s egg, and the other half from your father’s sperm (if nothing goes wrong, that is). Since females have two X chromosomes, all eggs get an X chromosome–because females don’t have anything else to give. Males have an X and a Y, so half the sperm a man makes have an X, and the other half have a Y.

Because of this, it is the sperm that determines a baby’s sex:

Now, you might already be starting to see why a man can’t give his son the baldness gene. The baldness gene, again, is on the X chromosome. Dad’s don’t give their sons an X chromosome, they give them the Y–that’s what makes the baby a boy. So father’s can’t give their sons any traits that are on the X chromosome.

Boys inherit the baldness gene from the X chromosome that they get from their mothers. She may have gotten that X chromosome from her father, though. So an angry bald man could blame his bald grandfather if he really wanted to (but it still might have come from his grandmother).

The baldness gene being on the X chromosome also explains why baldness is more common in men than in women.

Baldness is recessive. None-baldness is dominant. If you have one gene for “bald” and one gene for “not-bald,” you will not be bald, because “not-bald” is dominant. The only way to go bald is if you have 2 “bald” genes, or 1 “bald” gene and… a Y chromosome that doesn’t have this gene at all, so nothing to mask the “bald” gene.

Women have 2 X chromosomes, so they have 2 chances to get the non-baldness gene. For a woman to go bald, both her X chromosomes would have to have the baldness gene on it. The baldness gene isn’t that common, so the odds of getting two X chromosomes with the baldness gene are pretty small.

Men, however, only have 1 X chromosome, so if that 1 X chromosome has the baldness gene, they don’t have another X chromosome that can save them. That’s all they get.

Now, if you’re a man and you’re wondering if you are someday going to go bald, look at your mom’s family. If she has a brother who is going bald, you have a 50% chance of going bald too. But don’t worry, you can use rogaine. What you can’t do it use rogaine thinking that you inherited baldness from your father. Not cool.