Our Neanderthal Cousins
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RESEARCH HIGHLIGHTS E VOLUTIONARY GENOMICS Our Neanderthal cousins The complete mitochondrial genome was genome assembly, for which the phylogenetic techniques, the authors sequence of a 38,000 year-old authors designed a specific procedure also showed that the divergence time Neanderthal confirms that our closest for ancient DNA that allows gaps to between Neanderthals and modern hominid relatives did not contribute be ‘filled in’ where coverage is low. humans is 520,000–800,000 years. significantly to the mitochondrial This involved aligning sequences The ratio of non-synonymous to DNA (mtDNA) lineage of extant with the extant human mitochon- synonymous substitutions in the humans, and that the two groups drial genome, which established an Neanderthal lineage was unusually diverged about 660,000 years ago. overall picture of how stretches of high for primates, implying limited Pääbo and colleagues extracted Neanderthal mtDNA fit together. purifying selection and low effective mtDNA from a Neanderthal bone This information was then used to population size in Neanderthals. that was discovered in Croatia in design primers for PCR and Sanger The technical advances in this 1980. One of the technical challenges sequencing to fill in the missing study will be crucial for sequencing they needed to meet was ensuring pieces. the Neanderthal nuclear genome. sufficient sequence coverage so that The authors found 206 single It will be interesting to see if that bases were not miscalled because of nucleotide differences between genome gives similar results for contamination with modern the Neanderthal sequence and a divergence times, and whether more human DNA or degradation of the reference human sequence, only definite signs of lineage-specific ancient DNA (a process that can lead a few of which were located in the selection can be observed. to C to T transitions) — a feat that 13 coding mitochondrial genes. This Patrick Goymer was achieved using high-throughput level of difference is substantially 454 sequencing technology. The greater than that within modern ORIGINAL RESEARCH PAPER Green, R. E. et al. A complete Neandertal mitochondrial genome authors also kept contamination human sequences, strongly indicat- sequence determined by high-throughput levels very low using specialized ing that the two lineages have not sequencing. Cell 8 Aug 2008 (doi:10.1016/ clean-room facilities. The next hurdle mixed. Using standard molecular j.cell.2008.06.021) NATURE REVIEWS | GENETICS VOLUME 9 | SEPTEMBER 2008.