JB Anderson

University of Toronto, Mississauga, Canada

Mutation is the source of all allelic variation in populations. How sexual and asexual populations of organisms in nature evolve with mutation has been a subject of considerable debate for many years. Most estimates of mutation rate in natural populations have been indirect; they are based on the frequencies of alleles whose precise origins are unknown, and are dependent upon simplifying assumptions. Diploid genetic individuals of Armillaria gallica thought to be at least one million mitotic cell generations old (around 1000 ;years) offer a rare opportunity to detect and estimate the rates of mutation and mitotic crossing over in selected genomic regions under natural conditions. Each individual of A. ;gallica arises in a unique mating event and then grows vegetatively to colonize a territory that can vary in size and shape. In effect, the history of genetic change within the individual is evident in a spatial pattern reflecting growth from a point of origin. In parallel studies, we are also examining genetic change in experimental populations of the diploid yeast Candida albicans founded from a single cell. I will discuss the impact of mutation and mitotic recombination in populations of fungal plant pathogens.