When I get a new mystery DNA match—unknown connection, possibly no tree at all—the first thing I check is how much DNA they share with me in centimorgans, the unit we use to measure autosomal DNA. I can then plug that number into the Shared cM Project Tool to get a sense of which relationships are possible and, more importantly, which are most likely.
Next, I want to know which of my other DNA relatives the mystery person matches. All of the main testing companies provide this information, variously called “Shared Matches” (AncestryDNA), “Relatives in Common” (23andMe), “Shared DNA Matches” (MyHeritage), or “In Common With” (Family Tree DNA).
Ideally, I want to know not just that my mystery person shares DNA with, say, Cousin Bryan but also how much DNA they share with Cousin Bryan. Conveniently, both 23andMe and MyHeritage include that information in their tools; AncestryDNA and Family Tree DNA do not, for privacy reasons.
What’s a girl to do if she really wants that information from an AncestryDNA match? Ask them!
AncestryDNA recently started including the amount of DNA (centimorgans and number of segments) on the main match page. I initially reach out to my mystery matches with some possible surnames and to ask if they’re willing to collaborate to find the connection. If they reply, I ask them to click on Shared Matches with me, copy the entire page, and paste it into a message back to me. (Pasting might not work on a tablet device, but it should work on a computer.)
It’s easy for them, and it lets me see our shared matches from their perspective. I can then provide them with some quick feedback on the possible connection.
I recently used this trick with an adoptee who matched a client of mine. I’d already built a descendant tree of about 20 matches for the client, so when the adoptee sent me the shared match list, I knew exactly where she fit in. In fact, I identified her birth father within 5 minutes—my new record!