The reason why is, I thought, that they're tracing paternity via the Y-chromosome which gives a relatively clear path of male descent the same way that mitochondrial DNA is used for maternal descent.
I don't follow this logic, though.
So you can take a sample from a guy right now. But whose ancestry doesn't go through at least a few crucial women at some point?
By which I mean, eg: my brothers are men. But their only direct connection to our Polish great-grandfather is through our mother and then her mother, daughter of the Polish chap.
Surely that is overwhelmingly true of all men trying to track back to a particular population, yes/no?
Your brothers are certainly descended from your grandfather, but they didn't get his Y chromosome, because that came from your father. The 'gender chromosome' has two options. XX and XY. When we reproduce, we give half our chromosomes to the child (mixed with half of the other person's chromosomes).
So women have XX chromosomes, and men have XY. I passed my Y chromosome to my son - if I'd passed my X to him, he'd be a gril. Arborwoman gave him one of her two Xs, either the one from her mother, or the one from her father. So he's an XY. I know his Y came from me, which came from my dad, which came from my paternal grandfather - and so on. Because there's nowhere else to get them from - moms have XX chromosomes.
So there's no way for your maternal grandfather to pass your brothers his Y chromosome - it comes from the paternal side. Your brothers do have a 50% chance of having his X chromosome, but that's a separate issue.
So, they trace Ghengiz through his Y chromosome. That means a direct paternal link all the way down the chain. Yes, every one of those men has an X that he got from his mom, but the Y is the same Y the GK passed along to his kids. He didn't pass it along to his daughters - he gave them an X chromosome instead.
All that to say that the language is not some archaic patriarchal nonsense, but just a scientist speaking clearly. He's not denying the existence of the women (every man has an X after all), it's just a separate issue.
Does that help?
I know there's a way to trace maternal lineage as well, but it's a bit beyond my limited knowledge of genetics - My explanation comes from my recollection of a genetics course I took about 15 years ago.
