Max Planck Institute for Dynamics and Self-Organization -- Department for Nonlinear Dynamics and Network Dynamics Group
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MPI Kolloquium

Wednesday, 20.04.2011 16:15 c.t.

Why do viruses have Sex?

by Prof. Dr. Richard Neher
from MPI for Developmental Biology, Tübingen

Contact person: Jan Nagler


Ludwig Prandtl Hörsaal, Am Faßberg 11 AI-Gebäude


Almost all known organisms, even tiny viruses, often exchange genetic information with one another, i.e. reproduce sexually. Sex and recombination allows to bring together beneficial mutations that arose in different individuals. Furthermore, recombination helps separating the good mutations from the much more frequent deleterious mutations. Recombination thereby facilitates adaptation. In large populations, many mutations of either kind exist, resulting in a complicated evolutionary dynamics of many competing and interacting mutations. I will show that the speed of evolution in such a population is limited by and increases strongly with the rate of sex. While recombination speeds up evolution in many cases, it can be detrimental when fitness depends on specific combinations of genetic variants, which are disrupted by recombination. Competition between selection for synergistic combinations and recombination can give rise to a transition separating qualitatively different regimes. At supercritical recombination rates, the population consists of genotypes that are a nearly random assemblies of the available genetic material. Below the transition, the population condenses into a small number of fit genotypes that compete against each other. One of the best organisms to study these ideas empirically is HIV, which evolves so rapidly that substantial evolution can be observed over a couple of years. We are currently analyzing time series of HIV populations with novel sequencing techniques, which allow a detailed characterization of the evolutionary process.

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