Question about yDNA result if 3X GGrandfather is same person as 2X GGrandfather

[familydar]

An autosomal test would be your best bet for estimating generational difference.  It will depend on other proven blood relatives having tested, so matches can be found, but is by far the commonest and cheapest DNA test out there.  Lots of players, we all have our preferences who to test with, but to get the widest exposure you should upload your test results to as many additional databases as possible.

Jane :-)

[sugarfizzle]

No paternal test will be able to differentiate between the two generations. It will just be a case of tracing the male line as far back as possible.

An autosomal DNA test might be able to differentiate, depending entirely upon who has tested.

The 3G grandfather (Tom) might also be the 2G grandfather, I think is what you are saying, though I find your initial post quite difficult to follow (brain cells getting older by the minute!).

Different descendants of 4G grandparents, i.e. siblings of Tom, would expect to share X cM, and descendants of Tom might usually be expected to share half X cM, but would share X cM in this case.

Trouble is, this far back, the autosomal DNA amount inherited cannot be guaranteed, could vary greatly between different descendants naturally.

Another scenario is that Tom's descendants from his daughter might bring in another surname as likelihood father of her child.

I think the family lore will possibly remain as such, and perhaps that is how it should be.

Regards Margaret

Modified
Got it slightly wrong, but you will get my drift, hopefully.

Most recent common ancestors, MRCA, will be Tom and his wife/partner, 3G grandparents, not Tom's parents as I wrongly said before. This is the case, whatever happens after. So it is descendants of Tom and his wife who might or might not appear closer to the person who gets tested.

I still think it unlikely that autosomal DNA will give you the answer you are looking for unless another surname crops up as likelihood father of her child.

Regards Margaret