Sunday, October 15, 2006
Few Clues About African Ancestry To Be Found In Mitochondrial DNA
Mitochondrial DNA may not hold the key to your origins after all.
A study published in the open access journal BMC Biology reveals that fewer than 10% of African American mitochondrial DNA sequences analysed can be matched to mitochondrial DNA from one single African ethnic group. There has been a growing interest in the use of mitochondrial DNA to trace maternal ancestries, and several companies now offer to analyse individuals' mitochondrial DNA sequences to obtain information about their origins. The current study suggests that only one in nine African Americans may be able to find clues about where their ancestors came from, in their mitochondrial DNA.
Bert Ely from the University of North Carolina, and colleagues from other Universities in the USA analysed a database of the human variable region, or HVS-1 region, of mitochondrial (mt) DNA sequences from sub-Saharan Africa. [Science, Genetics, Mitochondria, mtDNA, Sahara]
Ely et al.'s results show that more than half of the African American HSV-1 sequences were found in many different sub-Saharan ethnic groups. Forty percent of the African American HSV-1 sequences did not match any sequences in the database and fewer than 10% were an exact match to a sequence from a single African ethnic group.
Source: BioMed Central
African-American mitochondrial DNAs often match mtDNAs found in multiple African ethnic groups
Bert Ely, Jamie Lee Wilson, Fatimah Jackson and Bruce A Jackson
BMC Biology 2006, 4:34
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 10% 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.
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