Málstofa: Einar Bjarki Gunnarsson

October 6, 11:40
Room N-130
Speaker: Ejnar Bjarki Gunnarsson (University of Iceland)
Title: The site frequency spectrum of a neutrally evolving tumor
Abstract: The site frequency spectrum (SFS) is a popular summary statistic of genomic data, recording the frequencies of mutations within a given population. While the SFS of a constant-sized population undergoing neutral mutations has been extensively studied in population genetics, the advent of cancer genomics has attracted interest in the SFS of an exponentially growing population. In this talk, we derive exact expressions for the expected SFS of a cell population that evolves according to a birth-death branching process, first for cells with an infinite line of descent and then for the total population, evaluated either at a fixed time (fixed-time SFS) or at the stochastic time at which the population reaches a certain size (fixed-size SFS). We also derive limit theorems which characterize the first-order behavior of the fixed-time and fixed-size SFS under a more general Galton-Watson branching process. We finally show how our results imply consistent estimators for the extinction probability (ratio between the rates of death and birth) and the effective mutation rate of a birth-death process.