Understanding second cousin predictions from AncestryDNA?

Question

I have three extremely high second cousin predictions from my father's side. I do not know my anything about my biological father (Name, age, etc..).

My top matches are:

• R - 619 cM across 39 segments
• D - 401 cM across 28 segments
• E - 347 cM across 26 segments

All three are common matches with each other. E and R share 256 cM. E and D share 63 cM.

R is 35yrs old, D's age is unknown, and E if 54 years old. I am 28.

I've spoken with R whose parents died when she was eleven. (Not a lot of information given besides that)

E does not know her father's side either. We were able to figure out that I am related to her through her father's side and not her mom's.

Based on cM, is it possible that R is a half-aunt or even a 1st cousin?

Answer 1

I recommend you use the Shared cM tool at https://dnapainter.com/tools/sharedcmv4 to see the likelihood of possible relationships. A shared cM result can only suggest a group of relationships (or several groups with varying likelihoods). Each group has several possible relationships which the cM result cannot distinguish. For example, the 619 cM of the result with R shows a group which includes relationships of Great-great-(Aunt/Uncle,Niece/Nephew), Half-great-(Aunt/Uncle,Niece/Nephew), Half-1st-cousin, and 1st-cousin-once-removed.

This group of relationships is only some of the possible ones; the tool shows that this group has about a 52% chance of including the correct relationship. The tool also shows that a second group of relationships has a 44% chance of being the right group, a third group has a 3% chance, and two more groups are possible but have near-0% chance of being right.

You will need to use other information to narrow down the possibilities. Helpful data may include ages, some known relationships, and circumstances. Shared cM results of the people involved with other people can also indicate which relationships are more likely.

Answer 2

You have some decent matches here. Your next step is to find out the cM totals for each of the other people in relationship to each other. Unfortunately, Ancestry does not give you that information (just like it doesn't have a segment mapper). You will need to ask your matches to tell you the cM total for each of the other two (I'd also ask each to tell you the name and cM number for anyone else they match over 200 cM). You do not need the number of segments.

Use the Shared cM Project chart for the numbers (I prefer it to getting probabilities...I'd rather see the numbers for myself).

• R could be a first cousin, but D and E can not.
• D and E can be second cousins, but R can not.
• They could all be first cousins once removed.
• They could all be half first cousins.
• R could be a half aunt, but D and E can not have similar relationships to you.

There are a few other possibilities, but those are the main ones.