Truly that's just a count of the number of differing base pairs, which makes complete sense. This isn't that complicated. I'm sure you could argue it isn't the most RELEVANT figure that a geneticist would be concerned with, but, I think it's fair to say that's what they would take it to mean. I'd love to know if I'm wrong about that.

It's binary data, run a diff and give me the count. Since we are talking about the number 24, if there's 24 base pairs out of the total different, it's just total / 24 = variance ratio.

Likewise, the average is simply: take any two people, could the number of base pairs differing in each or present in one and not the other. Do that many times between different people, that's the average.