Do men have a higher genetic variance than women?

Question

I've heard that with the distribution of our genome women have less variation on the bell curve than men. Is there any basis for this? It was my understanding that women have more genetic variation than men due to having two X chromosomes and there being more variation on gene expression within the X chromosomes. I've also seen a theory that with traits linked to genes on the X-chromosome in women being averaged across the genetic variants found on each of a woman's two X-chromosomes, this would reduce the likelihood of extreme traits (men have just one X-chromosome, precluding this averaging process). Is there any biological possibility for men to have more genetic variation than women, and if so what would be a potential reason for it?

Answer 1

Hey! It's been 5 years since you've asked this question, but better late than never!

If you mean phenotypically, then men absolutely have more variation. As you mentioned, men only have one copy of each chromosome, meaning any mutations have no backup and become expressed. For women, they have two X chromosomes, giving the potential chance to have an extreme mutation masked by the other.

If you mean genotypically, then women may have more variation due to having two x chromosomes. The mutations are still there, even if they're not expressed. Additionally, since the x chromosomes are a homologous pair, they can undergo recombination during the prophase of meiosis! This gives the chance for even more variation. That's not even including x-inactivation, where only one x chromosome is expressed in a cell and the other is shut off at random.

In summary: phenotypically, due to women having a backup, men express more variation. Genotypically, due to the reasons listed, women pay have more variation. What a great question! Well done.