My research program focuses on understanding the genetic basis of evolutionary change. In particular I am concentrating on two major components of the evolutionary process. Firstly, I study how genetic differences among individuals lead to variation in the numbers and survival of their offspring (fitness). Secondly, I determine how those genetic differences can become partitioned between populations when they begin to diverge genetically into different species. Salmonid fishes (Atlantic salmon, Arctic charr, rainbow trout, brook charr) continue to be the models for most of this work because their biology makes them interesting candidates for genetic analysis. To address the first component, I am studying the action of natural selection to determine how variation among individuals in measurable traits (phenotypes) leads to differences in the numbers and survival of their offspring. However, to understand how this selection might drive the evolution of phenotypes it is also necessary to appreciate how genetic differences among individuals result in phenotypic differences. I therefore examine the genetic bases of phenotypic traits, both by determining the relative contributions of genetic and environmental effects to their variation, and by identifying regions of the genome that affect their expression. This information is being integrated into the selective breeding programs of several economically important species for aquaculture. Comparative analyses are being done to examine the fate of genes after genome reorganization. Conventional approaches for locating important genes within the genome require families of known brothers and sisters to be used in laboratory-based studies. I am also employing a novel approach in which genetic information is used to reconstruct family relationships in wild populations so that the genes affecting phenotypes can subsequently be identified. To address the second component I examine different forms (morphs) of Arctic charr that differ in both appearance and ecology, and live together in Icelandic lakes. By studying genetic variation in natural populations, and also by carrying out long-term laboratory and field experiments I use these fish to answer questions on the role of such physical variation in promoting the formation of groups that do not mate with each other. In particular I am determining the way in which these different forms might have arisen, and also investigating the role of such forms in the origin of new species. Finally, inventories of genetic markers in economically important species (walleye, cod, sturgeon, trout, charr) are being used to answer questions relevant to their management and conservation.