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The origin of modern humans is a heavily debated issue that scientists have recently tackled by using mitochondrial DNA (mtDNA) sequences. One hypothesis explains the limited genetic variation of human mtDNA in terms of a recent common genetic ancestry, implying that all modern population mtDNA originated from a single woman who lived in Africa less than 200,000 years ago.
Mitochondrial DNA sequences, like the Y chromosome, do not recombine and are inherited from the maternal parent. This lack of recombination allows sequences to be traced through one genetic line and all polymorphisms assumed to be caused by mutations.
Mitochondrial DNA in mammals has a faster mutation rate than nuclear DNA sequences. This faster rate of mutation produces more variance between sequences and is an advantage when studying closely related species. The mitochondrial control region (Displacement or D-loop) is one of the fastest mutating sequence regions in animal DNA.
The ability to isolate mitochondrial DNA (mtDNA) from palaeontological samples has allowed genetic comparisons between extinct species and closely related nonextinct species. The reasons for isolating mtDNA instead of nuclear DNA in fossil samples have to do with the fact that
mtDNA, because it is circular, is more stable and degrades slower then nuclear DNA.
Each cell can contain a thousand copies of mtDNA and only a single copy of nuclear DNA.
While there is still controversy as to whether Neanderthals are direct ancestors of humans or evolved independently, the use of ancient genetic sequences in phylogenetic analysis adds an interesting dimension to the question of human ancestry.
Ovchinnikov, I., et al., 2000. "Molecular analysis of Neanderthal DNA from the northern Caucasus," Nature 404(6777), pp 490-493.
Sajantila, A., et al., 1995. "Genes and languages in Europe: an analysis of mitochondrial lineages," Genome Res. 5 (1), pp. 42-52 (1995).
Krings, M., et al., 1997. "Neanderthal DNA sequences and the origin of modern humans," Cell 90 (1), pp. 19-30.
Jensen-Seaman, M., and K. Kidd, 2001. "Mitochondrial DNA variation and biogeography of eastern gorillas," Mol. Ecol. 10(9), pp. 2241-2247.
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