system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do men go bald as they get older but women don't?
gpt
Genes code for proteins. Baldness is caused by a missing or malformed protein, caused by what we'll call the baldness allele. The version of the gene that makes the protein for hairiness can be the hairy allele.

If there's one copy of the hairy allele present, the recipe is there so the protein can be made properly and nobody goes bald. If there's no copy of the hairy allele, only the baldness one, you go bald.

Men have one X chromosome and one Y chromosome. Women have two X chromosomes. Each chromosome is made of multiple genes, each coding for different characteristics.

The primary gene for pattern baldness is on the X chromosome. Since the Y chromosome lacks an opposing gene (being significantly shorter), there's no way for the hairy allele to be on the Y chromosome. One copy of the baldness allele is enough to cause male pattern baldness.

Women *can* go bald, but they need two of the baldness allele (one on each X chromosome), so it's much rarer.