I am not a biologist or a geneticist, nor do I pretend to even understand, what I should. I think I have a working knowledge of DNA, enough to be dangerous..
Having provided my lack of bonafides, might I posit my question.
What happens to auDNA after say the 10th generation
As I understand it, there is not enough bits of DNA left after the 9th generation (counting self as gen 1) to predict any sort of a relationship.
Eventually, with each succeeding generation, what bits there are, are halved, eventually the contribution is so negligible as to not be "readable".
I do understand that DNA is not precisely halved with each reproduction.
Anymore than my siblings and I receive the exact same chromosones from each parent, otherwise all siblings would be copies, (exception the Baldwin brothers)
But with a halving at each generation, it would seem that at some point in time a particular chromosone, would virtually disappear from a lineage.
To put it this way. I descend from Charlemagne (supposedly, as perhaps do most western Europeans), however Charlemagne's auDNA will not show up in my profile, not even with triangulation.
While it might have disappeared completely in my line, another person could have a snippet in their genetic profile. But there is no way of Identifying which SNP('s) came from Charlemagne.
While it appears that some auDNA SNP's do in fact fall out during the reproductive process, over generations, new DNA is not created during the reproduction process, however there should be mutations, just as there are mutations in Y and mtDNA. (I'm merely theorizing, not postulating).
These mutations could (should?) appear as new SNP's, then again do SNP's mutate?
I apologize if I sound confused, because I am. I am really trying to grasp this science.
Why would two people who share a 4th great grandparent, and the same YDNA, not show up as 5th cousins?
And how can three people whose, common (paper) ancestor be a 7th or 8th great grandparent, show up on family finder as 4th cousins remote?
Yet at Y67, he shows up at a GD of 2 and 3 to these same people (they are nephew and uncle)
At Y67 he shows up at a GD of 0 to two people, whose common paper ancestor would be a 7th or 8th great grandfather.
But he does not show up as a Family Finder match on either of his Y67 GD=0. On the other hand he shows up as a 4th cousin remote to two people whose common ancestor (if one's claimed genealogy is correct) would be a 7th - 9th great grandfather., but their YDNA match at Y67 is at a GD of 2 and 3.
I apologize for the confusion, but the confusion is all mine.