Martin Agis, PhD student

Identification of local selective sweeps

The origin of Drosophila melanogaster is thought to be in Africa from which it colonized the world about 10,000 to 15,000 years ago. As Drosophila spread into new continents, it settled habitats which differ with respect to food resources, climate and other environmental parameters. Thus, different populations were exposed to different selection regimes and local adaptations to the new environments may have ocurred. Such adaptations should leave footprints within the genome of an organism. Consider a gene carrying a new mutation that provides a new allele which is selectively favourable compared to the ancestral one. Under directional selection this particular gene would rapidly increase its frequency within the population until it becomes fixed. This process is called a selective sweep.

Microsatellites are highly polymorphic, codominantly inherited and highly abundant in all eukaryotic genomes. This makes them attractive for use in kinship and paternity testing as well in population genetics. Due to their high mutation rate, microsatellites show large variation. Although most microsatellites are presumably neutral, a microsatellite locus linked to a gene which is under directional selection would also be affected. Therefore, the microsatellite allele linked to the favourable allele of the gene would spread through the population and the variation at this particular microsatellite locus would be reduced. This phenomenon is called hitchhiking. As microsatellites are distributed across the whole genome, several microsatellite loci could be affected by hitchhiking processes. I am searching for these traces of selective sweeps in natural populations of D. melanogaster by scoring variation at microsatellite loci.


Microsatellites are now well established as a genetic marker to address questions in population genetics. I am interested in inferring population structure and dynamics in natural Drosophila melanogaster populations. To study genetic distance, gene flow and the demographic history of a recently colonized continent, I am investigating Australian populations which were collected along the east coast of Australia, from New South Wales to Tasmania.

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