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I was adopted and have known my birth family for many years. I just did a DNA test and found I have 702 matching cM's with the daughter of my mother's brother (making her my 1st cousin). This helps validate my mother.

However, I DO NOT match any relatives of my supposed birth father. They divorced before I was born.

I am being shown two 2nd cousin range matches with 419 & 468 cM's. They are a brother and sister. We have talked and are trying to understand if their father's brother could be my father.

If so, wouldn't they be 1st cousins also, like on my mothers side?

Their matching cM's are almost half of those of the matching 1st cousin on my mothers side. That leads me to believe my father is in their family but another generation back. Perhaps he is their grandfather or on of his brothers.

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Your 702cM match falls in the 553 to 1225 range that you would expect for 1st cousins.

Your 419cM and 468cM matches fall below the 553 to 1225 range that you would expect for 1st cousins.

However, they fall well within the range to be expected for half 1st cousins which is 137 to 856.

To understand what is meant by half first cousins I recommend reviewing How much DNA should I share with a half-first cousin?

If my grandmother was unfaithful to my grandfather, then my half-first cousins (the children of my mother’s theoretical half-sibling) would not share my grandfather’s relatives as DNA matches. Specifically, my half-first cousins should not match my grandfather’s first cousins, their children, or their grandchildren.

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