Influence of evolutionary forces and demographic processes on the genetic structure of three Croatian populations: A maternal perspective

Background: Many Croatian islands are examples of genetic isolates, with low level of heterozygosity and high level of inbreeding, due to practice of endogamy. Aim: The aim was to study the genetic structure of two insular and one mainland population through high-resolution phylogenetic analysis of mitochondrial DNA (mtDNA). Subjects and methods: MtDNA polymorphisms were explored in 300 unrelated individuals from Mljet, Lastovo and the coastal city of Dubrovnik, based on SNP polymorphisms. Results: All mtDNA haplogroups found in the sample were of typical European origin. However, the frequency distribution of their subclades differed significantly from other Croatian and European populations. MtDNA haplotype analysis revealed only two possible founder lineages on Mljet and six on Lastovo, accounting for almost half of the sample on both islands. The island of Mljet also has the lowest reported haplotype and nucleotide diversity among Croatian isolates and the island of Lastovo, a new sublineage of a usually quite rare U1b clade. Conclusion: The results can be explained by the effect evolutionary forces have on genetic structure, which is in line with the specific demographic histories of the islands. An additional research value of these two island isolates is the appearance of certain Mendelian disorders, highlighting their importance in epidemiological studies.