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Research Overview

Dawn Marshall

1) Gene discovery and the genetic basis of inherited disease in non-model organisms

This builds on previous work identifying genes linked to phenotypic traits in mammals, including the gene and mutation associated with white coat colour in Kermode bears. The focus on non-model organisms is a strategic one, because many wild species are evolutionarily more closely related to humans than are model organisms. As a consequence they share many inherited diseases with similar genetic causes. A specific example of this is the condition hereditary gingival fibromatosis which presents in humans as an overgrowth of the gingival tissues leading to functional and aesthetic difficulties. Silver foxes, Vulpes vulpes, manifest a similar condition called hereditary hyperplastic gingivitis (HHG). Research is currently underway to discover the gene and mutation associated with HHG in foxes. This project utilizes resources available from the human and dog genome projects.

2) Evolutionary history of mutations and rates and patterns of DNA sequence evolution

I am also interested in the origins of mutations and the historical and evolutionary factors such as natural selection or founder events that explain their current frequency and geographic distribution. For example, I am investigating the evolutionary history of LINCL (late infantile neuronal ceroid lipofuscinosis) mutations in the founder population of Newfoundland, to determine whether a founder event is necessary and/or sufficient to explain the prevalence of this condition on the island, as opposed to another explanation such as natural selection via heterozygote advantage.

A related question is what factors determine rates and patterns of DNA sequence variation in different genes and genomes. How DNA variation is disseminated in the genome is interesting in its own right, and understanding the factors shaping such patterns is necessary when DNA polymorphisms are used to infer the evolutionary history of organisms. In this context, I compared rates and patterns of evolution of genes in the mitochondrial genome of chaffinches, and identified mutational hotspots in the control region sequences of these birds. Along with colleagues, I found evidence for recombination in the chloroplast genome of lodgepole pine, a result which has significant impact on how we interpret genetic variation in this genome. And, as part of the fox gene discovery project, B.Sc. Honours student Sara Tully is conducting a molecular evolutionary analysis of the SOS1 gene, a candidate gene for hereditary hyperplastic gingivitis in silver foxes.

3) Phylogeography and evolutionary history of populations inferred using neutral genetic variation

Neutral polymorphisms in DNA allow us to delineate organismal history from the level of the individual, family, and population (microevolution) to species and higher taxa (macroevolution). I use DNA sequences to investigate the historical demographics of populations and subspecies of organisms such as Kermode bears, chaffinches and lodgepole pine, focusing on factors like changes in population size, range expansions, and ongoing gene flow. Phylogeography, the study of the distribution of genetic lineages with respect to geography, is a crucial aspect of this process. Understanding population structure and history is vital to the conservation and management of resource species. In this context, the phylogeographic origins of brook trout (Salvelinus fontinalis) in southeastern Labrador are being investigated in my laboratory in collaboration with the Department of Environment and Conservation Wildlife Division.