Sharing 1.5% and 1.3% DNA, - half cousin once removed and half second cousin?

Question

Hello everybody,
I am searching for my deceased mothers unknown father and have found two pretty close matches, mother and son, but the "half"-relative aspect is confusing me (I don't have my mothers DNA-test, only her half-sisters and she's not related to my two matches).

The lady is same age as my mother and her son is the same age as me.
My match with the lady: 1,5%, total 104,4 cM, six segments, longest 44,6 cM.
My match with her son: 1,3%, total 90,4 cM, four segments, longest 44,7 cM.

p.Normal {margin:0.0pt; margin-top:0.0pt; margin-bottom:0.0pt; margin-left:0.0pt; margin-right:0.0pt; text-indent:0.0pt; font-family:"Arial"; font-size:10.0pt; color:Black; font-weight:normal; }MyHeritage suggests the lady is my "1st cousin twice removed - 3rd cousin once removed" and that her son is my "3rd - 4th. cousin".

While acccording to _isogg.org/wiki/Autosomal_DNA_statistics
"1.563% and 106.25 cM", would make them both my "Second cousins once removed, half second cousins, first cousin three times removed, half first cousin twice removed" (though, the son a bit further related).

Now, am I correct assuming the lady is my mothers half cousin and her son my half second cousin? Meaning, the lady's uncle is my mothers father and my grandfather?

Also, I have a tiny bit jewish ethnicity which does not stem from any of my other three grandparents. The lady seem to have no such ethnicity, but her sons fathers family are jewish. I've found +/-30 matches with her son (most of them are not shared with her) and through them a huge number of distant matches who are jews. Would this and the (to me seemingly) relatively small difference between 1.5% and 1.3% match suggest that I'm also related to his fathers family?

I'd be very grateful for any help, thank you!
Line

p.Normal {margin:0.0pt; margin-top:0.0pt; margin-bottom:0.0pt; margin-left:0.0pt; margin-right:0.0pt; text-indent:0.0pt; font-family:"Arial"; font-size:10.0pt; color:Black; font-weight:normal; }

Comments

Does anyone know the answer to my first question? If it's correct that the lady is my mothers half cousin and her son my half second cousin. In other words that the lady's uncle is my mothers father/my grandfather?
Thanks again!

Answer 1

If you match with both a parent and a child in a parent-child pair, your cM shared with the child will not necessarily be half the cM shared with the parent, as it is rather random which segments of DNA the child has received from each parent.

Since your tests are at MyHeritage, you can use their chromosome browser (under DNA Tools) to see exactly which segments you share with the mother, and which segments with the son. Only if at least one of the segments you share with the son is not also shared with the mother can you conclude that you are related to the son through the son's father as well.

Comments

Wow, thank you so much! That's interesting, I wasn't aware of that. Yes, we share a small piece of 6,3 cM on a chromosome where I share nothing with his mother.
Holy moly, that sure explanes a lot! And raises a billion new questions