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nodeciapalabras OP t1_iv0g35u wrote

Reply to comment by SweetBasil_ in Why don't we have Neandertal mitochondrial DNA? by nodeciapalabras

Can we know for sure there isn't any neanderthal mitochondria in any human being with the sample taken in the studies?

At the same time, I can't really understand why if there is a 2% of neanderthal DNA in our bodies, there isn't any neanderthal mitochondria survivers in our bodies. To me, it just seem so remote thinking that there isn't any female straight line to survivors, if we can't explain it in terms of fertility...

I know that I am probably not seeing the full picture, I need much more information to understand it. I just can't find it right know.

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Foxs-In-A-Trenchcoat t1_iv0h1vr wrote

20%??? More like 1-2%

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bitwiseshiftleft t1_iv0qutr wrote

The 20% figure is very relevant though. Per Wikipedia, an estimated 20% of distinctly Neanderthal genes are still extant.

The process here is not that different from mtDNA. When a couple produces a child, each gene from either parent has a roughly 50% chance to be passed to that child. (Ignoring mutations, where the gene might eventually become unrecognizable. Also its chance of being passed on further depends on whether the gene is adaptive or not, but let’s assume it’s neutral.) MtDNA is different, in that it is always passed from the mother, but the child has a roughly 50% chance to be female and thus to be capable of passing on those genes. Chromosomal genes can swap between chromosomes, but this mostly doesn’t affect the 50% probability of each gene being passed on. So the statistics for mtDNA (as a whole since it doesn’t recombine) and for other genes should be roughly similar, perhaps with different rate constants (eg due to men having a wider variation in how many children they have).

In any case, if only 1/5 of distinctly Neanderthal genes have survived this process, it’s not too surprising that their mtDNA didn’t make it (as far as we know).

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Tanagrabelle t1_iv0icpt wrote

Not sure if this will help, but if I understand correctly, it goes like this:

Let's say a woman has only sons. The sons have her mitochondrial dna, and have children. The grandmother's mitochondrial DNA is left behind because, apparently, when the sperm hits the egg, it destroys the mtDNA it carried with it. And, because nature is devious, that doesn't always happen completely. But usually, then the grandchildren will have only their mothers' mitochondrial DNA. However, any of the granddaughters will have their paternal grandmother's X chromosome.

And for further fun, because our chromosomes line up and split apart without regard to whether they came from the mother or the father in the first place, a grandchild might easily have very little from one or another of their grandparents. Like the time the father had passed away, and his mother was sure one of the grandchildren wasn't his child. The DNA test didn't detect enough relation to the grandmother, so they tested against the siblings, which worked because they were full siblings, not half.

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