Clinal variation in the nuclear DNA of Europeans

Allele frequencies are clinally distributed for many protein polymorphisms in Europe, suggesting that the current populations are derived from an ancestral group that expanded from the Near East. It is not yet fully established whether that expansion took place during the Neolithic or earlier or whether the detectable protein variation faithfully reflects the underlying molecular variation. In this study we address the latter question by describing geographic patterns of genetic diversity at seven highly polymorphic DNA markers. Two of these markers are minisatellites, four are microsatellites, and the seventh is a locus of the HLA system. By analyzing a database of 304 samples, with more than 130,000 chromosomes, we found evidence for a major clinal component of genetic variation. At most loci spatially close populations resemble each other genetically, and the degree of genetic similarity, as measured by spatial autocorrelation statistics, decreases at increasing distances. The observed patterns of molecular variation do not seem to differ qualitatively from those identified for protein polymorphisms. This suggest that low levels of population structuring, described in some mitochondrial DNA studies, may reflect different evolutionary histories for nuclear and maternally inherited markers or, alternatively, that spatial patterns of mitochondrial DNA variation may need more sensitive statistical methods to be recognized.