Kužela seminar series

Fri 27 Nov. 2009, 14:00

Title: Detecting natural selection with empirical codon models
Speaker: Carolin Kosiol, Veterinärmedizinische Universität Wien

The statistical modelling of the evolutionary process is of great
importance when performing systematic studies, because it enables us
to make inferences about evolutionary relationships of genes, proteins
and genomes and organisms of particular interest and to study the
processes and pressures of molecular evolution itself.

The estimation of empirical codon models sheds new light on recently
discussed questions about biological pressures and processes acting
during codon sequence evolution. My results show that modelling the
evolutionary process is improved by allowing for single, double and
triple nucleotide changes; the affiliation between DNA triplets and
the amino acid they encode is a main factor driving evolution; and the
nonsynonymous-synonymous rate ratio is a suitable measure to classify
substitution patterns observed for different proteins. However,
comparing models estimated from genomic data and polymorphism data
indicates that double and triple changes are not instantaneous.

This new view of how codon evolution proceeds leads to consequences
for selection studies. I will discuss that under the new empirical
codon model purifying selection is less purifying and that cases of
positive selection are observed weaker than under the standard condon
models (Yang et al.,Genetics 155: 431-449 (2000)).