very low cm for 2c1xr but share matches on both sides

[weenie]

Hi, i never questioned this until recently understanding more about DNA and CMs.

my nana had a sister sent to Canada as British home child, her son to unknown , had few more kids and i match these 2 grandchildren, i shall call A and B

i have access to A dna , i also have my full bro, half bro and his daughters DNA and also a 3rd cousin DNA on my  nana's maternal line.

i share 53cm to A, and 51cm to B
full bro to A 14cm and to B 46cm
half bro to A 28cm and to B 39cm
niece to A 14cm and to B 31cm

so i thought either my nana or her gt nana have different fathers. so not James arthur Peaker.

however upon recieving A DNA they have over 30 common ancestor matches that i can confirm and in the tree backed up to Peaker line, but not 1 of those matches match me, my brothers or niece.

i have 2 common ancestor DNA Matches that i can fit in the tree, but non of my brothers or A and B match them.
my brother has 1 common ancestor DNA match i can correctly put in tree again no match to anyone else, and my half brother has 1 but i cant confirm as hit and miss with details. but non of us share the match.

the matches me and my brothers have, do have shared matches and links to our nanas maternal side that do match A and B.

all out shared matches are on My nana's maternal side, same with 3rd cousin. where we have 100's between us.

so am i right in thinking that my Nana may have  unknown father - or is it just very weakend DNA passed down?.

my nana was the youngest and her mum left the family when nana was 2 leaving to James Arthur Peaker to look after the children, hence how her sister was a british home child.

any help greatly appriciated

Weenie

[Biggles50]

First look at your post and my immediate thought, half relationships.

That would explain the cM values.

At these levels the process of DNA recombination very much comes into play with the segments being inherited by one person and not by another.  So yes, one can be a biological relation with someone and yet share no DNA or very low unreported levels.

The same with shared matches and it is one we have experienced, my Wife has two DNA matches who are distant cousins of hers but 2C’s to each other, the Grandson of my Wife’s 1C has only one of them as a DNA match so yes he is related to both of them but does not share DNA with one of them.

Hope this helps if you are burning the midnight oil.

I’ll revisit your post tomorrow after a good nights sleep.

[4b2]

It's useful to add a pictographic tree, when outlining these relationship. It becomes difficult to process all the information.

I put the post into Grok and it gave the attached tree.

The more work with DNA, the more I see that cM is not overly important. What is important is if you can find the multiple lines of Ancestry in a DNA tree.

I go with what is presented here - https://dnapainter.com/tools/sharedcmv4

Even though that data can be polluted by errors or unknown half relationships. 14-51cM are in the 2C1R range.

I also have a 14cM 2C1R. I initially thought that it must be due to a half relationship. And it did appear that I had no matches to show my relationship to one of our shared lines. But neither did the 2C1R, or another 2C1R.

After some digging I found there were matches for this line I thought was probably incorrect by infidelity. But with more digging I found there were matches for that line that were either: 1) double matches with another line, 2) in a cluster with smaller cM.

[weenie]

Thankyou, A and B are one generation up on image.

im just going through some larger cms of unknowns where i dont know where they belong.... so far on full brothers over 2000 -

Weenie