Interpreting DNA Results from 23andMe?

Question

I received my results from 23andMe and I read and read and I just don't understand.

I wondered if you could help me?

My Mother is 91 years old and never knew who her birth father was. We took the 23andMe DNA test but I am having a hard time understanding it.

She got a hit to a man, named John, on her Mother's side; 5.07% 13 segments.

My numbers in relationship to this John were, 2.26% and 6 segments.

We are thinking that this John's grandfather could be my Mother's father. However could it also mean that one of John's brothers could also be the missing father.

Answer 1

There is a very useful table of average percentage sharing for relationship on the ISOGG Autosomal DNA statistics page. It shows the average (across a great number of different people, in theory) shared percentage value and the most common relationships the percentage is associated with. Any particular relationship of two particular people will have a shared value different than this (up or down).

From that table we see that your mother's match to John of 5.07% falls between these two groups of relationships:

My guess is that 5% would be a bit more likely to be an instance of a 6.25%-group relationship, but could be from the 3.125% group of relationships. The particular details of possible relations can influence the likelihood of the relationships. For instance, your mother's age and John's age will suggest some are more likely. If the relationship goes back to someone who might have had children by two different partners, the "half" relationships would be more likely. (If you want a reference for relationship terms, there are many available, such as this one.)