mtDNA polymorphisms in five French groups: importance of regional sampling

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Abstract
According to classical markers, France has been reported to be regionally heterogeneous. Here, we propose to test the homogeneity of the French mitochondrial gene pool by analysing D-Loop and coding regions polymorphisms in 210 individuals stemming from five regions. The data set obtained was also used to test the ability of mitochondrial DNA to detect well historically established admixtures (admixtures between British/Irish people and native Breton people in our case). For these purposes, the sampling procedure was subject to special care, concerning the individuals' geographical origin and maternal pedigree. The mtDNA analysis revealed some regional specificities in haplogroup distribution, which is discussed in terms of successive settlements of France. Statistical analyses were conducted to investigate mtDNA diversity and structure within and between British, Irish and French groups. They tended to show affinities between Morbihan region and Britain plus Ireland. Furthermore, genetic evidences were in line with the fact that Morbihan region results from an admixture event, agreeing with historical evidences of successive migrations from Britain and Ireland into Brittany. These results also tended to outline the fact that two geographically very adjacent samples (Morbihan and Finistère), sharing a cultural and linguistic area, can present a distinct genetic pattern. Although mtDNA analyses were able to identify a historically reported admixture event, we point out here the high influence of the sampling procedure and representativeness over the migrations hypothesis. We also underline the importance of regional sampling for studies on the spread and/or origin of specific European haplogroups (here U5a1a and U8).