Help me understand this...
I got a DNA match with a 3rd or 4th cousin. The ancestor we have in common is my aunt. However, her son is not listed as a someone we have in common?
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DNA is random. Your cousin inherited half from his mother, you inherited some from that same family line. Your 3rd and 4th cousins randomly didn’t inherit The same chunk as your cousin. Happens all the time in more distant relationships. 2nd cousin and closer without shared DNA means there’s a secret somewhere, anything beyond that can just be the randomness of DNA