Slate released a story a few days ago that will be a surprise to many readers. Sometimes 23andMe reports an inaccurate DNA relationship between two testers. This revelation will come as a shock to some people but was not to me.
I’m a genetic counselor who specializes in analysis of DNA results from ancestry tests. In my work with clients, I have come across situations of a DNA relationship between two people being reported incorrectly. Sometimes it’s impossible to tell and the circumstantial evidence and further testing of other family members is needed to figure it out.
The Slate piece goes into more detail about how 23andMe makes determinations, much of which was new information to me. 23andMe includes the reported age of the testers, for example, as one piece of information that goes into determining relationships. There are obvious problems to this approach, given that men can father children for about six decades (teens into their 70s) and women for three or four (teens into their 40s, possibly later with fertility assistance).
Half siblings can be dozens of years apart in age, same as cousins. A niece can be older than her aunt, and a nephew can be older than his uncle. There are many instances of mothers having their youngest children after they have become grandmothers. Long story short, age is a poor measure to use in guessing relationships.
Other DNA test companies get around this by listing relationships as ranges. AncestryDNA, for example, might list someone as “close family” to you but will be vague about the exact relationship. That approach a much wiser way to go, of course.
The Slate article reports that 23andMe developed a resource page for people with unexpected discoveries and matches at some point this year which I only learned of as a result of the Slate article. Disclosure: this website (watersheddna.com) is listed as a resource on the page, which also was news to me when I first saw it.
Hopefully given the spreading awareness of problems with DNA matching, more people will connect with my services, find a professional genetic genealogist through a forum like ISOGG, discover my book or others similar to it, and find online places (like aforementioned ISOGG) where they can learn more about DNA relative matching to do their own deeper dive.
I’ve written more about this in past posts as well. It’s important not to react quickly in a time of surprise and shock. You need the full information about an unexpected DNA result before you know exactly what is going on.