Confused about cousin relationship determination

Question

I have a solid hypothesis about my mother's bio parents, but am confused about determining the probability of my theory.

I have 268cM in common with my DNA relative. I plugged that into DNA Painter and determined that the following relationship probabilities apply (just focusing on the ones that are likely in my hypothesis):  

  - 61% 2C, 1C2R,

  - 21% 2C1R, 1C3R

  - 18%:  1C1R

The relationship I'm testing is this:

My mother is my DNA Relative's cousin.

me >> Mom >> presumed GP >> brother of presumed GP [my great uncle] >> son of brother of presumed GP [the known DNA relative]

Would this be my 2C if my hypothesis is true?

When I try plugging relationships into the cousin chart from my DNA relative's perspective I get:

Target  >> his father >> father's brother >> his child (my mother)  >> me

In looking at the cousin chart, I keep ending up with the relationship of 1C1R. What am I doing wrong?  2C and 1c1R are not the same proababilty.

Answer 1

Link to a relationship 'tree'

I always find a tree helps

Comments

Great tree, Heather, Thanks.

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Thanks Heather! That chart is great. I had always seen/used a different version of the chart (like on DNA Painter). The version I used had a blank spot below Great Uncle, and before 2C. I see from the tree version you provided that that blank spot would be a 1C1R relationship.

This means that my hypothesis has an 18% probability, as opposed to 61%. Another possibility is if it was a Half 1C1R. Sometimes these 'half' relationships aren't well known/shown in family trees.

Answer 2

me >> Mom >> presumed GP >> brother of presumed GP [my great uncle] >> son of brother of presumed GP [the known DNA relative]

Would this be my 2C if my hypothesis is true?

NO - that is a 1C1R relationship. He is your mothers first cousin and you are 1 generation removed.

Target  >> his father >> father's brother >> his child (my mother)  >> me

In looking at the cousin chart, I keep ending up with the relationship of 1C1R. What am I doing wrong? 

There is nothing wrong. 1C1R is the correct relationship in that situation.

What proof do you have for the second cousin relationship?

Second cousins have the same GREAT grandparents in common, not the same grandparents.

Comments

I think where I was going wrong, is that I was misunderstanding the common relationship tree that is used on DNA Painter. That blank spot between Great Uncle and 2C confused me. But on the chart that Heather linked to in her response, I see that that blank spot should be labeled 1C1R.