Response to Misleading Comments in the Sarah Tishkoff Paper Published in Science April 30, 2009
Recently a paper, “The Genetic Structure and History of Africans and African Americans” was published in Science magazine by Tishkoff et al. This paper studied 1,327 nuclear microsatellites in 121 African populations, 4 African populations and 60 non-African populations. One analysis in the study explored the use of these nuclear markers for tracing ancestry of AAs. The markers failed to allow differentiation of AAs into various west African ethnic groups. The statement in the paper that has been depicted by the media is: “Thus, most African are likely to have mixed ancestry from different regions of western Africa. This observation, together with the subtle substructure observed among Niger-Kordofanian speakers, will make tracing ancestry of African Americans to specific ethnic groups in Africa challenging, unless considerably more markers are used.”
This statement is in reference to the use of microsatellite markers for inferring African ancestry for AAs. This study has no relevance to what we do at African Ancestry. The study did not study Y chromosome and mtDNA. We do not use nuclear markers like Tishkoff et al. did in this study. Each nuclear marker is found on one of the 23 pairs of human chromosomes, varies, and has two copies (alleles), inherited one from each parent. Due to this complex inheritance pattern it is difficult to determine which allele is inherited from which parent. The mixing of alleles make their use for tracing ancestry difficult.
In fact, over 5 years ago I discovered that using these types of nuclear markers will not be informative for tracing ancestry of African Americans given their mode of inheritance and the diverse west African ancestors who were enslaved in the Americas. During the research for the PBS special African American Lives it was found that the markers are not informative for WA ancestry. When scientists used nuclear markers to trace AAs, like Dr. Henry Louis Gates and tried to place them in a group or region he and the other AAs always clustered in the middle of the groups suggesting that AAs have very mixed West African ancestry.
The problem with testing nuclear markers reveals the importance of lineage based markers for uncovering ancestry. It is the same logic as traditional genealogy tracing for family history. You start with one person, one lineage and build the tree by adding additional lineages. This is practical and reveals that we all have multiple ancestors in which can identify with. For mtDNA and Y chromosome tests these lineages represent those maternal and paternal ancestors. They allow for a more focused connection (a single direct lineage) with ethnic populations.
We educate our customers about the multiple lineages that make up our ancestry. Given our mixed ancestries it is best to test as many lineages as possible in order to get a better picture of your overall ancestries. You will be more successful if you have as much information about your family tree (pedigree) as possible. This will allow us to identify different people in the family to test for more information.
- Dr. Rick Kittles, African Ancestry