Genetic diversity in northern Spain (Basque Country and Cantabria): GM and KM variation related to demographic histories.

Genetic diversity in Northern Spain (SW Europe) was assessed through the analysis of the GM and KM immunoglobulin markers in 505 individuals using a set of 17 allotypes, including the G2M(23) allotype which has been infrequently used before now. The individuals were representative of three anthropologically well-defined populations belonging to two geographically and archaeologically distinct areas in the Basque Country (Guipúzcoa and Alava provinces) and to the mountainous region of Montes de Pas in the province of Cantabria. Gene frequency distributions indicated a high genetic divergence between Montes de Pas and the Basque Country, and a relative degree of heterogeneity between the two Basque regions. The genetic differentiation of Montes de Pas, which is consistent with previous classical polymorphism analyses, suggests a considerable genetic variation range within the Iberian Peninsula, possibly higher than that often polarised around the Basque versus non-Basque variation. Analyses of genetic structure show that the major differentiation of Montes de Pas could be related to the historically documented mixed origin of this population. The moderate genetic distances between regions in the Spanish Basque Country could be explained by differential systematic pressures acting through a stronger gene flow in the South than in the more isolated Northern areas. The comparisons with neighbouring populations from the French Pyrenees suggest that the present genetic variation revealed by lg polymorphisms in SW Europe can be related to historical demographic processes including gene flow and/or low population sizes.