Ancestry DNA questions

[elizabethgaslight]

A few questions for people who have done Ancestry tests, or have more detailed knowledge about how to interpret the results:

I have a second cousin, one grandparent in common, both of us on Ancestry. Our DNA results show 35cM shared DNA. On Ancestry's explanatory info that level of match suggests 4th cousins. Does anyone know if there's a big margin for error, or is it more likely that our grandparents (who were siblings) had different fathers?

Did people find that more matches appeared a few weeks or months after doing the test? I have quite a few people with some common DNA but can't see how they fit into my tree. I'm wondering, as with the 'hints' if I'll get more useful info over time?

How useful have others found the DNA test for bridging gaps in your trees where you didn't know an ancestor's father? I was hoping this might help as I have three grandparents with no father on their birth certificate. One in particular was born in a small village, so I hoped I might get matches for unknown relatives from the same area which might help me work out who the father was likely to be, but that might be unrealistic.

2nd cousin... you mean great-grandparent in common?

yes the % match can be diverse. It's just a sample not a comprehensive comparison. I have a 3rd cousin who I can't find on my daughter's Ancestry DNA account, but there he is an obvious close relative on my uncle's Ancestry account.

I found a 'long lost' uncle by cross matching with 2 relatives on my grandmother's side (and only to her, not matching with other relatives/branches I could identify).

New people join Ancestry all the time so yeah new data can come in, at any time.

If it is saying 4th cousin then that would mean you share a common GGG grandparent. If you know that this person is definitely your second cousin you can amend the relationship.
With my research confirmed 2nd cousins have 352cm shared for one and 246cm for another and my 4th cousin has only 36cm shared with me, which is less than 1% shared DNA.
DNA isn't passed down completely evenly and there is some margin of variance on the totals. Sometimes ancestry has told me this person could be my 3-6th cousin and unless you have a tree and research you can line up against each and confirm it can be difficult.
They do upgrade the results periodically. It is also worth testing the next generation up if you are able, we knew there was an Indian link 6x back but it was so small it didn't come up on one generation but by testing the next one back we got enough to confirm.

Ignore ancestry suggested relationships. They aren't that useful.

Use this tool instead:

dnapainter.com/tools/sharedcmv4

A second cousin relationship isn't on the list that I can see so is extremely unlikely.

These are the most likely relationships:

5C3R † 6C 6C1R 5C 6C2R 4C1R 5C1R 7C Half 3C2R 4C2R 5C2R 7C1R 3C3R 4C3R 8C or more distant

Much more distance that 2nd cousin.

There are some half and "removed" 2C relationships coming up as possibles.

Half 2C is on this list - 3% probability.

Sorry, I meant we have (I think) two great grandparents in common - our grandmothers were sisters. But I'm wondering if they are likely to have had different fathers, given the low cM.

Thanks for the dnapainter link. I'll have a good look at that later and work out what the possibilities are.

I think the most likely thing is that one of our two grandmothers (who were sisters) had a different father than the one listed on her birth certificate. I see from dnapainter that other hypotheses score higher, but I think that would have to have involved something like one of those two grandmothers really being the child of an aunt or cousin and passed off as my great grandparents' child. I know that was not an unusual situation, but in this case it would have involved naming the wrong mother on the birth certificate - is that likely? There's not enough of an age gap between the children of the family for an older sibling to have had a child which was raised by grandparents as their own.