Professor Sykes discusses M-DNA and the y chromosome

Teacher:
Is there a part of DNA that's passed exclusively down by fathers?

Professor Sykes:
This M-DNA which I've been talking about and which I've used, I guess mostly, is passed down by mothers from mothers to all the children actually. But sons don't pass it on, men don't pass on M-DNA. The reason being that M-DNA's found in eggs and not in sperm really, essentially. And so when an egg is fertilised, although the other DNA in an embryo and in everybody, comes equally from father and mother, the M-DNA only comes from the mother.

But you asked about whether there was a piece of DNA that comes down through the father's line and indeed there is, it's called the y chromosome and father's pass y chromosomes onto their children. In fact, the y chromosome is carried in the father's sperm and half the sperm from a male, doesn't matter if it's human or any other animal, half the sperm's got a y chromosome and the other half hasn't. So if an egg is fertilised by a sperm containing the y chromosome then it will turn into a boy and if it's fertilised by a sperm that doesn't contain a y chromosome then it will turn into a girl.

And interestingly enough, the natural pattern of human embryo development is to be a girl, so you have to do something active to stop embryos turning into girls. So in fact, in a few cases, although embryos will have a y chromosome, if that y chromosome doesn't work very well, then the embryo will still turn into a girl.

So there's no doubt really when you come down to it that actually women, females, are the, if you like, fundamental sex and that men are genetically-engineered women.