Extent of heterogeneity in mitochondrial DNA of sub-Saharan African populations

Variation in the mitochondrial DNA (mtDNA) control region as detected by sequence-specific oligonucleotide (SSO) probes is described for 381 individuals from nine sub-Saharan African populations. Population diversity estimates for SSO types ranged from 0.23 to 0.97, while 102 SSO types were detected, none of these types was shared by more than four populations. Eighteen types occurred in > or = 10% of individuals in some populations; of these, 11 were population-specific. One type occurred in 15% of the total sample, but was shared among only three populations. African SSO types were characterized by high frequencies of blank variants, indicating that there was additional variation present at the nucleotide sequence level in regions where SSO probes hybridize. Analyses of molecular variance (AMOVA) incorporating genetic distances between SSO types showed that 30% of the total variation was due to differences among populations, indicating that there is statistically significant heterogeneity (p < 0.001). An AMOVA on mtDNA control region nucleotide sequence data from 12 populations showed that including all additional variation present at the sequence level increased the variance due to population subdivision to 34% (p < 0.001). Overall, when considering both the low diversity within some populations and high heterogeneity among populations, SSO typing of mtDNA may not be a desirable forensic DNA typing method for continental African populations. Further mtDNA sampling of African-derived populations of North America should be carried out to determine how much of the continental African mtDNA variation is of forensic significance. However, the existence of extensive mtDNA control region nucleotide sequence variation in African populations means that control region sequencing is still appropriate in forensic cases requiring mtDNA analysis.