finding DNA link with adoptee, only negative results!

[ejblom]

Hi all,

I've encountered some strange DNA testing results, I hope there is somebody who can provide an explanation....

Together with an adoptee that I found on 23andme, we have been busy finding other family members that also match him. So far, I have tested 5 family members and they all came back negative.

It started out with a match on 23andme, predicted 3rd-6th cousin, one segment, 0.32%. Since then, I've uploaded my data on GEDMATCH and FTDNA and know this big segment comprises of ~ 24 cM.

I've attached my DNA testing scheme to this post, but it also available here.

I'll present my tested persons chronologically, otherwise they don't make any sense. As you can see, I first tested my dad. No match with my dad, so I match the adoptee via my mom.

Some background info: the adoptee has strong suspicions that he is connected to Holland paternally. He also has a lot of (distant) hits with US members, so most probably a maternal ancestor from the USA.

With this in my mind, I focused on descendants of distant family members that emigrated a long time ago. The following persons got tested (or were found to be already present in public DNA databases):

II - A running story in my family was about two brothers who left Holland and went to the USA. I tracked down the descendants and found one willing to get tested. No match.

III - After uploading to GEDMATCH, I found a DNA cousin (3rd cousin 1R) who did not match the adoptee, so I could discard another link.

IV - Another US family member that I discovered. We got in touch and he was willing to have himself tested. No match.

At that time, I realised my strategy wasn't working. I decided to zoom out and find close family members.

V - 1st cousin 1R, niece of my mom on my granddad's side. No match

next, I was lucky to have a great aunt on my grandmother's side. At this moment, we were positive that she should come back positive since we already eliminated my granddad's side by testing V.

VI - great aunt on my grandmother's side...... NO match!

(all tests did have a DNA match with myself, so good positive controls).

So at this moment we are not sure what to think about this scenario. No hit on my grandmother's nor granddad's side.

Since my great aunt is 2 generations up, her results are more trustworthy than the results of my 1st cousin 1R.

Can anyone explain this?

My thoughts on this are that probably my mom only has the same shared percentage of DNA with the adoptee as myself. This might also be true for my granddad. In this scenario, my 1st cousin 1R on my granddad's side might have received nothing, just by chance.

Last note, I did perform the phasing tool on GEDMATCH. This discarded a small region (~5 cM), but the largest autosomal segment was still intact.
In addition, I also have another great aunt on my granddad's side who is still alive (106 years old!).

[Canyon Wolf]

Keep searching for cousins!

I think the only thing you can say with certainty is that the adoptee is not on your father's side. The only reason you know this is because you are matching the adoptee with your phased data and there is no match with your father's DNA.

The only inheritance that is certain is that you get 50% from mom and 50% from dad. You should get approx. 25% from your grandparents, but because recombination is a random beast there is no guarantee you will get anything from a specific grandparent. The more generations involved the more likely you get 0 from any specific ancestor. This applies to you and to every other person you test. The randomness of recombination is also responsible for making certain 2 siblings do not get the exact same combination of DNA from their parents unless they are identical twins.

So, with this in mind, your non-matches with the adoptee do not eliminate whole branches of the tree because the person tested simply may not have inherited the same DNA as you did from the MRCA you share with the adoptee.

I hope this helps.

You are a wonderful person to get so involved with helping this adoptee. I wish you the best.

[ejblom]

worst case scenario?

I think the only thing you can say with certainty is that the adoptee is not on your father's side. The only reason you know this is because you are matching the adoptee with your phased data and there is no match with your father's DNA.

The only inheritance that is certain is that you get 50% from mom and 50% from dad. You should get approx. 25% from your grandparents, but because recombination is a random beast there is no guarantee you will get anything from a specific grandparent. The more generations involved the more likely you get 0 from any specific ancestor. This applies to you and to every other person you test. The randomness of recombination is also responsible for making certain 2 siblings do not get the exact same combination of DNA from their parents unless they are identical twins.

So, with this in mind, your non-matches with the adoptee do not eliminate whole branches of the tree because the person tested simply may not have inherited the same DNA as you did from the MRCA you share with the adoptee.

I hope this helps.

You are a wonderful person to get so involved with helping this adoptee. I wish you the best.

Hi Canyon Wolf,

Thanks for the explanation. I can agree with most of your reasoning and it all makes a lot of sense. I do have a question concerning your remark concerning:

non-matches with the adoptee do not eliminate whole branches of the tree because the person tested simply may not have inherited the same DNA

Regarding the results of my great aunt (sister of my grandma). Let's assume the adoptee is related via my grandma. There could be a very small chance that the segment was transferred as a whole starting from my grandma. In this scenario, the same fragment could very well be not present in her sister (my great aunt).

However, and now comes a more practical issue, if this is the case, this means that the original prediction of my link with the adoptee is now also valid for my grandma. So, to the original 3rd-6th cousin prediction two generations should be added, making it a 5th-8th cousin.

I actually have ancestral data for most of my family lines (after a few weeks of ancestry clicking, so there might be some mistakes) but then to go back and find most promising family line or even father is a rather daunting task!