Looking for roots in Africa? DNA search not easy
WASHINGTON (Reuters) - African-Americans hoping to use DNA to find their roots may have to look harder than previously thought, researchers said on Thursday in a study they said shows Africans are too genetically mixed to make tracing easy.BMC Biology (open access)
Several companies now offer to help Americans trace their African ancestry using mitochondrial DNA, which is passed from mother to daughter virtually unaltered.
"What's your tribe?" asks one. "Trace Your Roots Back in Time," offers another.
But biologist Bert Ely of the University of South Carolina and colleagues found that fewer than 10 percent of African-American mitochondrial DNA sequences that were analyzed can be matched to any single African ethnic group.
The news might disappoint people who cannot trace a long paper trail of ancestors. More than 11 million Africans were forcibly shipped to the Americas during the slave trade that peaked in the 17th and 18th centuries.
"The test that everybody does is the same test and it is all valid," Ely said in a telephone interview.
"It is just that some companies will over-interpret the data and give you the most likely result instead of all of the matches."
Working with colleagues at the University of Massachusetts and the University of Maryland, Ely looked at 3,700 mitochondrial DNA sequences from people in sub-Saharan Africa.
African-American mitochondrial DNAs often match mtDNAs found in multiple African ethnic groups
Bert Ely et al.
Mitochondrial DNA (mtDNA) haplotypes have become popular tools for tracing maternal ancestry, and several companies offer this service to the general public. Numerous studies have demonstrated that human mtDNA haplotypes can be used with confidence to identify the continent where the haplotype originated. Ideally, mtDNA haplotypes could also be used to identify a particular country or ethnic group from which the maternal ancestor emanated. However, the geographic distribution of mtDNA haplotypes is greatly influenced by the movement of both individuals and population groups. Consequently, common mtDNA haplotypes are shared among multiple ethnic groups. We have studied the distribution of mtDNA haplotypes among West African ethnic groups to determine how often mtDNA haplotypes can be used to reconnect Americans of African descent to a country or ethnic group of a maternal African ancestor. The nucleotide sequence of the mtDNA hypervariable segment I (HVS-I) usually provides sufficient information to assign a particular mtDNA to the proper haplogroup, and it contains most of the variation that is available to distinguish a particular mtDNA haplotype from closely related haplotypes. In this study, samples of general African-American and specific Gullah/Geechee HVS-I haplotypes were compared with two databases of HVS-I haplotypes from sub-Saharan Africa, and the incidence of perfect matches recorded for each sample.
When two independent African-American samples were analyzed, more than half of the sampled HVS-I mtDNA haplotypes exactly matched common haplotypes that were shared among multiple African ethnic groups. Another 40% did not match any sequence in the database, and fewer than 10% were an exact match to a sequence from a single African ethnic group. Differences in the regional distribution of haplotypes were observed in the African database, and the African-American haplotypes were more likely to match haplotypes found in ethnic groups from West or West Central Africa than those found in eastern or southern Africa. Fewer than 14% of the African-American mtDNA sequences matched sequences from only West Africa or only West Central Africa.
Our database of sub-Saharan mtDNA sequences includes the most common haplotypes that are shared among ethnic groups from multiple regions of Africa. These common haplotypes have been found in half of all sub-Saharan Africans. More than 60% of the remaining haplotypes differ from the common haplotypes at a single nucleotide position in the HVS-I region, and they are likely to occur at varying frequencies within sub-Saharan Africa. However, the finding that 40% of the African-American mtDNAs analyzed had no match in the database indicates that only a small fraction of the total number of African haplotypes has been identified. In addition, the finding that fewer than 14% of African-American mtDNAs matched mtDNA sequences from a single African region suggests that few African Americans might be able to trace their mtDNA lineages to a particular region of Africa, and even fewer will be able to trace their mtDNA to a single ethnic group. However, no firm conclusions should be made until a much larger database is available. It is clear, however, that when identical mtDNA haplotypes are shared among many ethnic groups from different parts of Africa, it is impossible to determine which single ethnic group was the source of a particular maternal ancestor based on the mtDNA sequence.