SummaryThe majority of published human mitochondrial DNA sequence data are confined to hypervariable region I in the control region. By contrast, this paper focusses on a nucleotide site in hypervariable region II. Unlike most non‐European populations whose mtDNA sequences have been studied in the literature, the British ‘white Caucasian’ population has a high level of variation at site 73 (following the site numbering by Andersonet al.1981). This variation appears to have its origin largely in a mutation from guanine to adenine at that site with an estimated minimum age between 15000 and 25000 years. The data of Piercyet al.(1993) suggest that roughly half of the British ‘white Caucasian’ mitochondrial gene pool is descended from a common maternal ancestor who carried this mutation at site 73. This site also plays a central role in distinguishing the five major European mtDNA clusters identified in Richardset al.(1996). We suggest that the lineages carrying an A at site 73, together with some other lineages, may have their origins in a small founder population which expanded after the last glacial maximum about 20000 years ago. We conclude that, in addition to region I sequences, site 73 is worth determining in studies of Caucasian po
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