Jakob Christian Mueller

Most of the inhabitants of South Tyrol in the eastern Italian Alps can be considered isolated populations because of their physical separation by mountain barriers and their sociocultural heritage. We analyzed the genetic structure of South Tyrolean populations using three types of genetic markers: Y-chromosome, mitochondrial DNA (mtDNA), and autosomal Alu markers. Using random samples taken from the populations of Val Venosta, Val Pusteria, Val Isarco, Val Badia, and Val Gardena, we calculated genetic diversity within and among the populations. Microsatellite diversity and unique event polymorphism diversity (on the Y chromosome) were substantially lower in the Ladin-speaking population of Val Badia compared to the neighboring German-speaking populations. In contrast, the genetic diversity of mtDNA haplotypes was lowest for the upper Val Venosta and Val Pusteria. These data suggest a low effective population size, or little admixture, for the gene pool of the Ladin-speaking population from Val Badia. Interestingly, this is more pronounced for Ladin males than for Ladin females. For the pattern of genetic Alu variation, both Ladin samples (Val Gardena and Val Badia) are among the samples with the lowest diversity. An admixture analysis of one German-speaking valley (Val Venosta) indicates a relatively high genetic contribution of Ladin origin. The reduced genetic diversity and a high genetic differentiation in the Rhaetoroman- and German-speaking South Tyrolean populations may constitute an important basis for future medical genetic research and gene mapping studies in South Tyrol.

Summary: Association studies may request more details of a specific haplotype. Haplotype-specific decay of linkage disequilibrium is such a crucial and versatile characteristic. It may be used, e.g. to search for signals of natural selection in a risk haplotype. Here, we present a web-based tool to explore the relationship between population frequency and extended linkage disequilibrium measured as haplotype homozygosity of observed haplotypes within a specified candidate region. Availability: The web-tool is available at http://ihg.gsf.de/cgi-bin/mueller/webehh.pl

Assessing the patterns of linkage disequilibrium (LD) has become an important issue in both evolutionary biology and medical genetics since the rapid accumulation of densely spaced DNA sequence variation data in several organisms. LD deals with the correlation of genetic variation at two or more loci or sites in the genome within a given population. There are a variety of LD measures which range from traditional pairwise LD measures such as D′ or r² to entropy-based multi-locus measures or haplotype-specific approaches. Understanding the evolutionary forces (in particular recombination) that generate the observed variation of LD patterns across genomic regions is addressed by model-based LD analysis. Marker type and its allelic composition also influence the observed LD pattern, microsatellites having a greater power to detect LD in population isolates than SNPs. This review aims to explain basic LD measures and their application properties.

Since the mid–1980s the zebra mussel, Dreissena polymorpha, Pallas 1771, has become the protagonist of a spectacular freshwater invasion in North America due to its large economic and biological impact. Several genetic studies on American populations have failed to detect any large–scale geographical patterns. In western Europe, where D. polymorpha has been a classical invader from the Pontocaspian since the early 19th century, the situation is strikingly different. Here, we show with genetic markers that two major western European invasion lineages with lowered genetic variability within and among populations can be discriminated. These two invasion lineages correspond with two separate navigable waterways to western Europe. We found a rapid and asymmetrical genetic interchange of the two invasion lines after the construction of the Main–Danube canal in 1992, which interconnected the two waterways across the main watershed.