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cousin in common matches

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  • cousin in common matches

    Hello my cousin (who is only a cousin by a maternal grandparent) has 21 in common matches with me, 81 in common with my mother and 71 with my brother. In Ancestry we have only 2 matches. (no other family members tested there). Isn't that a normal amount of recombination?

  • #2
    Recombination is defined (in the FTDNA Learning Center Glossary) as
    Recombination is the mixing of the DNA on each chromosome that you receive from your mother and father. Different chromosomes and different parts of each chromosome are more or less likely to recombine in a single generation.
    You say your cousin is a cousin related by a maternal grandparent, so that means he or she is your 1st cousin, unless the sibling had a different father, in which case it would be a half cousin. He or she is the child of a sibling or half-sibling to your mother. If it's a full 1st cousin, you should be sharing an average of about 12.5% of your DNA (within a range of 8-18.5%), with an average of 900 cM (or a range of 575-1330 cM). You can check that at Ancestry and FTDNA. A half 1st cousin would share roughly half, or a bit less than half, of those amounts. I got those figures from the DNA Detectives Autosomal Statistics Chart, which can be found in a blog post by the DNA Geek, "The Limits of Predicting Relationships Using DNA."

    Your mother passed down 50% of her DNA to both you and your brother, but each of you received a different 50% (of her 100%). The same goes for your cousin from his or her parents, and between your mother and the parent of your cousin (your mother's brother or sister). So, your matches in common will vary. It also depends on how many of your known, and unknown, relatives have tested at any given company.
    Last edited by KATM; 5 December 2018, 01:59 PM.