A steep cline for mitochondrial DNA in Danish mice

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Abstract
Summary: One hundred and ninety-eight mice trapped along a south–north transect through the Danish hybrid zone betweenMus musculus domesticusandM. m. musculuswere typed for mitochondrial DNA (mtDNA), theYchromosome and ten autosomal loci encoding diagnostic proteins. The southern (domesticus) populations display two mtDNA variants (S1 and S2) and the northern (musculus) have a third mtDNA variant (N) ofdomesticusorigin. Across the hybrid zone defined by ten autosomal loci, there is a steep dine between the southern and northern types of mtDNA. As well as confirming an earlier finding that Danishmusculusall have adomesticusmtDNA (Ferriset al.1983a, &b), our results show that this mtDNA takeover is not the result of a persistent mitochondrial gene flow between the two subspecies. While the coincident dines for the ten autosomal loci and the abrupt dine for theYchromosome can be explained by selection, it is less likely to be the case for the mtDNA exchanges. We discuss the possible role of sex-linked migration and genetic drift to account for the distribution of the mitochondrial variants.