Confirming cM relationship groups for illegitimate child

[Susanna]

Hi all, I wanted to post my situation here to see if the more experienced researchers can advise me or point out errors. I'll get right to the science.

My father-in-law, living, was born illegitimately to a known mother (deceased). We have no idea who his father was. We tested him on AncestryDNA and found matches on both sides. Gedmatch dot com tells me that his parents were not related to each other. The AncestryDNA matches on his mother's side, who we were able to mutually confirm through oral history and photos, do not also match the family who would be his paternal lineage.

So far I have penciled out this family's tree, and I've corresponded a bit with one of the matches. The family had 6 children, and only one of the male children could have been old enough to father my FIL. Let's call the patriarch "Adam" and the eldest son "Aaron". (Edited to add: both are deceased.)

The AncestryDNA matches are

Person 1: 771cM; grandson of Adam on his mother's side
Person 2: 747cM; ID unknown
Person 3: 593cM; ID unknown
*Person 4: 558cM; great-granddaughter of Adam and great-niece of Aaron
Person 5: 406cM; grand-daughter of Aaron and great-granddaughter of Adam
**Person 6: 311cM; grand-daughter of Aaron and great-granddaughter of Adam
Person 7: 277cM; ID unknown

*Person 4 is Person 1's daughter
**Person 6 at some point also uploaded to gedmatch dot com, which yielded 337cM

My working theory is that Adam was my FIL's father, because he was only a few years older than the mother, while the age difference between Aaron and the mother was huge, but still scientifically possible.

If Adam was the father, then Person 1 would be a half-nephew of my FIL. If Aaron was the father, then Person 1 would be a full first cousin of my FIL.

Thank you for reading.

[prairielad]

Have you considered yDNA testing for him?
Depending on his surname (how common), ones yDNA STR Signature can be Surname specific.
It may give you an indication of his paternal lines Surname.

FTDNA does yDNA testing.(it is recommended to do at least yDNA37 for genealogical purposes)

Check out their Surname projects and see if his suspected Surname is part of the projects.

https://www.familytreedna.com/projects.aspx

[Susanna]

Thanks for the suggestion. The surname of the family isn't in the project (yet). We aren't opposed to doing more tests. We'd want to give that due consideration since it does cost money.

According to Adam's parents' census records, their ethnicity, combined with my FIL's mother's ethnicity, matches my FIL's "AncestryDNA pie chart" within a percent or two.

The only way I see someone other than Adam or Aaron being the father is if Adam and his wife had a male child together before they married and then adopted that child out.

We feel fortunate that Adam and Aaron's descendants happened to do AncestryDNA tests before we sent ours in. We could have ended up with nothing. I'll keep doing some reading about the tests here since I'm new to the site. Thanks!

[Ann Turner]

If I've plotted this out correctly, I don't think either scenario fits the amount of shared DNA very well. See the green chart in this blog post:

https://isogg.org/wiki/Autosomal_SNP_comparison_chart

Your FIL and #1 share the amount of DNA "expected" for 1st cousins. If Adam was the father, then your FIL and #1 would have an uncle/nephew relationship. If Aaron was the father, your FIL would be sharing more DNA with them than with #1.

Could Adam have a son by a previous marriage? That would make your FIL and #1 half-uncle/nephew, which would fit the amount of shared DNA.

[Susanna]

Hi, thanks for the reply. Is this the green chart?
http://thednageek.com/the-limits-of-...ips-using-dna/

Person 1 at 771cM is a "Group C" match. Person 1's mother (let's call her Jane) is a daughter of Adam and his Eve, and she is a full sibling to Aaron.

If Adam was the father, my FIL would be a half-sibling to Jane, and a half-uncle to Jane's son Person 1. I'm seeing half-uncle in Group C on the green chart.

If Aaron was the father, my FIL would be a full nephew of Jane, and therefore a full first cousin to Jane's son Person 1. This is also in Group C.

That's where I'm stuck scientifically, because even if Jane were to get tested (she's not deceased), it wouldn't rule out Aaron or Adam, because Jane and my FIL would be in Group B together, which includes both a half-sibling and a full nephew relationship. Whew!

If Adam had another son with a woman who was not his Eve, that child would only be a half-sibling to Jane. A son born of that male would be only a half-nephew of Jane and therefore a half first cousin of Person 1. That wouldn't explain how Person 1 ends up in Group C with my FIL, because half first cousin is in Group D.

That's why I still have as a viable option that Adam and Eve had a male child before they married and adopted that child out, and he was the father. As unlikely as that seems, it's scientifically possible. If that were the case, I would hope any descendants of that child would also be looking for family through DNA! Thanks again for the help.

(Edited to add that Jane told Person 4, who told us, that Adam was not faithful to his wife.)

[Susanna]

New data point: I have an ID on "Person 2" from my original post, who is a 747cM match to my FIL. This person's mother was another illegitimate child of "Adam", and I have confirmed this through genealogy research because Person 2's mother lived with Adam's parents when she was very young. There's also (sealed) record of a court case where Adam and the girl's mother were parties.

This is significant, because since we know Person 2 is a grandson of Adam, Person 2 can only be in the relationship group "half-nephew" to my FIL if Adam was *also* my FIL's father. In other words, if Adam's son Aaron was my FIL's father, then Person 2 would be only a half first cousin to my FIL, and at 747cM, the science doesn't support that.

In my second post to this thread I proposed the possibility that Adam and his bride had a male child together before marriage and they adopted that boy out, and he became my FIL's father. With the data point of Person 2's ID, this theory is now out the window. If "adopted boy" was my FIL's father, then my FIL would be a half first cousin to Person 2, but again, at 747cM, the science can't support that.

To recap: in my first post I ID'd 4 direct descendants of Adam who match my FIL's DNA. I'm now adding a 5th.

Am I missing anything? Thanks so much!