Cousin Prediction

A promising DNA match has appeared at 23andMe.com.  She shares a good chunk of chromosome 4 with my father and his three siblings.  As with all matches, I also check for DNA shared with my father's close relations.  If a distant cousin matches my father and his close cousin on the same segment of DNA, then I look for the shared ancestor in the branch of the family tree shared by my father and that cousin.  That is the strategy behind DNA testing not just yourself, but your aunts, uncles, and cousins.

You need to be careful when a distant cousin matches two close family members on different segments.  This could be indicative of two different ancestral lines, meaning that the distant cousin is not related to both close cousins by the same ancestors.

Beautifully illustrating this point, the promising match shares DNA not only with my father, but his mother's cousins and his father's cousin- on different segments.  To date, my research has not revealed any shared ancestors between my paternal grandparents.  (Though one of my grandmother's cousins shares a segment of DNA with my grandfather's cousin.)  This newest match may be connected in three different ways to my family, or maybe just two.

Hopefully a few generations of her family tree will be forthcoming and I can figure out the ancestor responsible for the chunk of chromosome 4.  My prediction:  third to fourth cousin.  IF she is related by a common ancestor to one of the grandparent's cousins, she should not be closer than a third cousin because they are the prior generation and their shared segment is too small for a second cousin range.

Segment Mapper by Kitty Cooper