Dual origins of Finns revealed by Y chromosome haplotype variation.

The Finnish population has often been viewed as an isolate founded 2, 000 years ago via a route across the Gulf of Finland. The founding event has been characterized as involving a limited number of homogeneous founders, isolation, and subsequent rapid population growth. Despite the purported isolation of the population, levels of gene diversity for the Finns at autosomal and mitochondrial DNA loci are indistinguishable from those of other Europeans. Thus, mixed or dual origins for the Finns have been proposed. Here we present genetic evidence for the dual origins of Finns by evaluating the pattern of Y chromosome variation in 280 unrelated males from nine Finnish provinces. Phylogenetic analysis of 77 haplotype configurations revealed two major star-shaped clusters of Y haplotypes, indicative of a population expansion from two common Y haplotypes. Dramatic and quite significant differences in Y haplotype variation were observed between eastern and western regions of Finland, revealing contributions from different paternal types. The geographic distribution and time of expansion for the two common Y haplotypes correlate well with archeological evidence for two culturally and geographically distinct groups of settlers. Also, a northeastern to southwestern gradient of Y haplotype frequencies provides convincing evidence for recent male migration from rural areas into urban Finland.