MITOCHONDRIAL-DNA SEQUENCE VARIATION ACROSS LINGUISTIC AND GEOGRAPHICBOUNDARIES IN ITALY

A previous investigation demonstrated the existence of extensive allel e frequency diversity within an area of northern Italy crossed by a li nguistic (dialect) boundary and by the Po River, either of them or bot h presumably constraining gene flow. We obtained hair samples from 45 school pupils from 9 localities in that area and sequenced a 255-bp se gment of the mtDNA D loop. Estimates of the minimum number of migratio n events from gene genealogies suggest that the Linguistic barrier imp aired gene flow more than the river did. However, an analysis of molec ular variance (AMOVA) showed that most sequence diversity occurs withi n rather than between populations and that the differences between gro ups of populations, defined either by linguistic or geographic criteri a, do not reach significance. Three areas of rapid genetic variation w ere identified; their locations suggest that populations of the wester n part of the study area evolved in relative isolation. Therefore mtDN A sequence variation does not seem to reflect the same processes-drift and presence of dispersal barriers-that led to the observed distribut ions of nuclear allele frequencies.