Monday, April 9, 2012

"Finding Your Roots with Henry Louis Gates Jr." - DNA in The Fourth Episode

Last night PBS aired the fourth episode of Finding Your Roots with Henry Louis Gates Jr. which featured husband and wife Kyra Sedgwick and Kevin Bacon. The episode concentrated on exploring the couple's deep American roots, stretching back to the early days of the Colonies.

Husband and wife Kyra Sedgwick and Kevin Bacon

Unfortunately, there was very little genetic genealogy in this episode. At the very end, Dr. Gates presented Kyra with her DNA results explaining, "Using traditional genealogy, we were able to trace her father's line back hundreds of years...but using DNA Analysis we were able to go even deeper into her past on her mother's line establishing her Jewish ancestry genetically." First Dr. Gates showed Kyra a chart. In editing they inserted a shot of a chart illustrating the path of Y-Chromosome DNA which is passed down from father to son. Since she is a woman and they were discussing her mother's side, I believe that they were actually analyzing her mitochondrial DNA haplogroup which is passed from mother to child. The voiceover said that they were looking deep into the past of her mother's line, so she likely has a mtDNA haplogroup that is associated with Ashkenazi Jews.

Chart from "Finding Your Roots" showing the path of Y-DNA

Then they looked at a chart from 23andMe's Ancestry Finder and Dr. Gates explained, "Here's a graph of your 23 chromosomes and what it says is that 50% of all of your genetic material that they examined traces back to Ashkenazi Jews."  Note that he adds the qualifier "that they examined". This is because the Ancestry Finder feature only reaches conclusions about the portions of your DNA that have people who match it in their system, so most people do not have 100 percent coverage on this tool. Ancestry Finder is based on the answers that your DNA matches provide on the 23andMe survey "Where Are You From?" and, therefore, bases its analysis on the stated birth places of your matches' grandparents. (For more information on this feature, please see the post that I wrote about Ancestry Finder when it was first introduced.) The Ancestry Finder feature allows a user to click a box to see which of their matches have self-identified their grandparents as Ashkenazi Jews. For Kyra, this was apparently the case with approximately 50% of her total matches on Ancestry Finder. Instead of showing a screenshot of the graph of her "23 Chromosomes" which would have illustrated this result, they showed an image of her Ancestry Finder list of matching populations (seen below). This list of matching populations identified by Ancestry Finder also supports Dr. Gates' team's conclusion that Kyra has substantial Ashkenazi Jewish ancestry since the ones at the top of the list are typical in my experience for  those with Jewish ancestry.

Kyra Sedgwick's 23andMe Ancestry Finder from "Finding Your Roots"

At the end of the episode, Dr. Gates revealed to Kyra that her fear of being cousins with her husband Kevin Bacon was confirmed and that she and Kevin are 9th cousins once removed. Although fun for entertainment purposes, in the context of genetics, this is pretty meaningless since chances are that neither of them has any genetic material remaining from their shared ancestor(s). If they were to both test their autosomal DNA at 23andMe or with Family Tree DNA's Family Finder, they would likely not find any significant common DNA between them (unless they have closer yet unidentified shared ancestors). Since Dr. Gates team likely did test them both at, at least, 23andMe, I suspect my assumption is correct. This is because with each successive generation of random autosomal DNA inheritance, the contribution of each ancestor gets broken into smaller and smaller pieces and the majority of our ancestors have "fallen off of our genetic family tree" by the time you reach back past a couple hundred years. (Blaine Bettinger of "The Genetic Genelaogist"explains this concept here.) That is why autosomal DNA tests for genealogy like 23andMe and FTDNA's Family Finder work best for researching more recent ancestry.

I am looking forward to next week's episode with Rick Warren, Angela Buchdahl, and Yasir Qadhi and hope to see more integration of genetic genealogy. In the preview, I caught a glimpse of my friend, 23andMe's geneticist Mike Macpherson (one of the creators of Ancestry Finder). I can't wait to see his appearance on the show!

Week 2 - Episode 3 - Barbara Walters & Geoffrey Canada


  1. Good history lesson, but so many missed opportunities to explain genealogy & genetic processes. :-( I do enjoy this show more than WDYTYA, though.


    1. Yes Kathleen,
      It seems that twice the content can be offered on Finding Your Roots as can be on WDYTYA because of the paucity of advertisements and lack of summaries coming out of each ad break.

    2. Yes, I agree with you both. It is nice that the show keeps moving forward and covers a lot of territory, but I do wish they would incorporate DNA more!
      Thanks for your comments,