Median-joining network of HVS-I haplotypes observed in 837 M9a'b mtDNAs. (a) mtDNA control region variations and/or certain coding region sites were considered to improve the resolution of the median-joining network. The variants are transitions, and transversions are further highlighted by adding suffixes A, C, G and T. "Y" means heteroplasmic status C/T, and "@" means a back mutation. The "†" labels the putatively ancestral node of haplogroup M9a'b. (b) The geographic origin of samples is shown by different colors corresponding to their respective locations on the map. For the samples from Tibet, the related population information is also noted.