Institute for Genomic Biology

Speaker

Michael Lynch

Michael Lynch is the Distinguished Professor of Biology and Class of 1954 Professor in the Department of Biology at Indiana University at Bloomington. Professor Lynch earned a Ph.D. in Ecology and Behavioral Biology from the University of Minnesota in 1977. He joined the faculty at Indiana University in 2001, and prior to that was at the University of Oregon.

The Drift-Barrier Hypothesis and the Evolution of Subcellular Features

Abstract:

A general principle in evolutionary biology is that the efficiency of selection declines with reductions in population size – once the level of refinement of a molecular feature attains the point at which subsequent beneficial mutations have fitness effects less than the power of drift, further steps toward molecular perfection are no longer possible. Hence, unless all beneficial mutations have large effects (unlikely), the limits to the evolution of molecular perfection will be more extreme in small populations. This drift-barrier hypothesis has general implications for all aspects of evolution, including the performance of enzymes and the stability of proteins. It also implies that effective neutrality is the expected outcome of natural selection, an idea first suggested by Hartl et al. in 1985. In the context of these arguments, I will discuss several aspects of genomic and proteomic evolution that appear to be governed by the stochastic effects of drift: 1) the inverse relationship between mutation rates and both population size and proteome size; 2) the substantial investment that cells make in surveillance mechanisms for error-prone processes; and 3) the diversity in oligomeric structures of proteins across the tree of life. Given our current understanding of the principles of genome evolution, we are now on the cusp of developing a theoretical framework for an evolutionary cell biology.

Research

Professor Lynch's research is focused on mechanisms of evolution at the gene, genomic, cellular, and phenotypic levels, with special attention being given to the roles of mutation, random genetic drift, and recombination. He utilizes several model systems, the microcrustacean Daphnia, the nematode Caenorhabditis, the ciliate Paramecium and its bacterial endosymbionts, the unicellular alga Chlamydomonas, the diatom Phaeodactylum, and numerous bacterial species.  In addition, comparative analyses of completely sequenced genomes are being performed to shed light on issues concerning the origins of genomic and gene-structural complexity. Most of the empirical work is integrated with the development and use of mathematical theory in an effort to develop a formal understanding of the constraints on the evolutionary process. Evolution is a population-level process, and the underlying philosophy of his research is that "nothing in evolution makes sense except in the light of population genetics."