Monday, May 14, 2012

"Finding Your Roots with Henry Louis Gates, Jr." - DNA in the Ninth Episode

The ninth episode of Finding Your Roots with Henry Louis Gates, Jr. featuring comedian Wanda Sykes, musician John Legend and 98-year old Margarett Cooper aired last night. Unfortunately, this was the shortest DNA segment of any episode so far (starting at 48:30), clocking just under two minutes. I have to admit that even without much genetic genealogy, I really enjoyed the thorough research tracing all three of these African Americans' family trees to their free ancestors of color. That was some outstanding genealogy work!

Although the genetic genealogy that was discussed in the episode was squeezed into a very small segment, I thought the explanations offered were very clear, so I will quote some of Dr. Gates' words here. In order to trace some of the guests' African ancestry back to its origin in Africa, the show used the company African Ancestry again. African Ancestry performs only Y-DNA and mitochondrial DNA (mtDNA) tests, so keep in mind that they are only examining the direct paternal and/or direct maternal ancestral lines.

The paths of Y-DNA (in black) and mtDNA (in red) in our family trees

Dr. Gates explains, "Fathers pass on exact copies of their Y-DNA to each of their sons and mothers pass on replicas of their mitochondrial DNA to all of their children." This means that the Y-DNA follows only the direct male line because fathers pass their Y-chromosome only to their sons. Conversely, mtDNA follows only the direct maternal line because only women pass their mitochondrial DNA on to their children. For example, if you are a female and have a brother, you share the same mtDNA that was inherited from your mother, but only you will pass it to your children, while your brother's children will receive their mother's mtDNA instead of his. (One caveat to Dr. Gates' statement is that both Y-DNA and mtDNA occasionally mutate, so they are not always "exact copies".)

Dr. Gates goes on to say, "So, if an African American shares either of these DNA segments with a member of a present day ethnic group in Africa, then it is likely that they share a common ancestor." It is on this basis that African Ancestry reaches their conclusions. (I commented on this idea further in an earlier episode.) In order to be able to do this, African Ancestry has compiled a database of samples collected from "the ethnic groups in West and Central Africa that were most heavily raided during the slave trade."

Map of the regions sampled for African Ancestry's DNA database

Each of Dr. Gates' guests were tested to determine to which tribe this small portion of their DNA most closely matches. Being male, John Legend was fortunate to be able to trace both his Y-DNA and his mtDNA. His mtDNA was most similar to the Mende people in Sierra Leone and his Y-DNA was most similar to the Fula people in Guinea-Bissau. As Dr. Gates states, this "suggests" that these specific branches of his family tree lead to these areas.

John Legend's mtDNA traces to the Mende People

John Legend's Y-DNA traces to the Fula tribe.

The women only had the opportunity to trace their mitochondrial DNA since they do not have Y-chromosomes. Wanda didn't seem to have received a very specific result. The show stated that her mtDNA matched several groups, including the Tikar and Fulani (appears to be the same as the Fula) people of Cameroon. Incidentally, without seeing her family tree, this demonstrates to us that her white ancestor Elizabeth Banks who mothered Wanda's line of free ancestors of color was not her direct maternal ancestor (mother's mother's mother, etc....). If she had been, Wanda would have likely possessed European mtDNA.

Wanda Sykes's mtDNA traces to the Tikar and Fulani people

As a side note, I thought it was a lot of fun watching the lovely Margarett fulfill one of her stated life goals by learning more about her ancestors before she dies. Her welcome inclusion in the show supports the idea that watching non-celebrities unravel the secrets of their family trees can be just as compelling (sometimes more so) than the stream of celebrities being offered these opportunities.

Margarett right after learning the origins of her mtDNA

Margarett was extremely pleased to discover that her maternal roots traced back to the Temne people of Sierra Leone. (I strongly suggest following the links to read about all of these interesting African groups.)

Margarett's mtDNA traces to the Temne Tribe of Sierra Leone

Let's not forget that in focusing exclusively on the Y-DNA and mtDNA, large portions of the guests' genetic heritage was ignored. My wishlist for this episode would have, of course, included the popular pie-charts with the ancestral origin percentages (admixture) for each of the guests. It would have been interesting to see how much European DNA each of these guests possess, as well as if there is potential for Native American ancestors in their family trees. Usually Dr. Gates uses 23andMe's Ancestry Painting for this, although he sometimes also uses Family Tree DNA's Population Finder as well. At the top of the list would have been an autosomal DNA test performed on John Legend's delightful fourth cousin John Hale to determine if they share any detectable DNA segments inherited from their mutual third great grandfather, the legendary Peyton Polly and his unknown wife. A test such as 23andMe or Family Tree DNA's Family Finder have about a 50% chance of detecting shared DNA between fourth cousins. As I have said before, the use of genetic genealogy in exploring these types of questions is my favorite application of the science. Autosomal DNA testing works best for examining a theory that two people are related to each other in relatively recent times. A negative result does not disprove the connection at this level of relatedness, but a positive one can strongly support it. Unfortunately, while Dr. Gates' team likely performed many of the DNA tests on my list, there wasn't time to show all of the results.

Sadly, next week is the last episode of the series, so I hope it is chock full of genetic genealogy! I don't know where all of us will go to get our television genealogy fix since "Who Do You Think You Are?" is also ending next week (apparently for good). I sure hope that Dr. Gates hurries up and produces another one of his great family history series!

For the last episode, Dr. Gates and his team will be exploring the multiracial ancestry of Michelle Rodriguez, Adrian Grenier and Linda Chavez. See you then!

I have been writing a review of the DNA testing used in each episode:
Week 1- Episode 1 & Episode 2 - Harry Connick Jr. & Branford Marsalis; Cory A. Booker & John Lewis
Week 2- Episode 3 - Barbara Walters & Geoffrey Canada

Week 3- Episode 4 - Kevin Bacon & Kyra Sedgwick
Week 4- Episode 5 -  Rick Warren, Angela Buchdahl & Yasir Qadhi
Week 5- Episode 6 - Robert Downey, Jr. & Maggie Gyllenhaal 
Week 6 - Episode 7 - Condoleezza Rice, Samuel L. Jackson and Ruth Simmons 
Week 7 - Episode 8 - Martha Stewart, Margaret Cho and Dr. Sanjay Gupta

1 comment:

  1. I was disappointed that their admixture hadn't been discussed, but like previous episodes, I really am impressed with the subject matter, the guests, and the thought processes behind each episode. Well done Dr. Gates.