Genetic drift in human evolution 1

Published on March 18, 2015   35 min

Other Talks in the Series: Human Population Genetics II

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This lecture is entitled Genetic Drift in Human Evolution. My name is Sohini Ramachandran. I'm a faculty member at Brown University in Providence, Rhode Island. And I'm a member of ecology and evolutionary biology in our Center for Computational Molecular Biology.
To give you an outline of what we're going to discuss today first I'll introduce genetic drift as the concept and define it. And then I'll talk about how in population genetics we might model genetic drift both through theory and also some illustrative simulations that will illustrate some theoretical principles. Then I'll discuss the signature of genetic drift on human population genetic data, so patterns that have been identified, mostly within the last decade, from studies directly done on humans living today. And I'll end by talking about how important genetic drift is and especially some future directions for studying the role of genetic drift in human populations. So first let's begin with introducing the concept of genetic drift.
As a field, the goal of population genetics is to study the change in the allele frequencies under the forces that produce and maintain genetic variation. So what exactly are these forces? Well, first there's mutation. And next migration, which is also called gene flow. Of course, natural selection is an important evolutionary force. And there are different types of natural selection. There's purifying selection which removes deleterious mutations from a population. There's adaptive selection that promotes the survival and reproduction of individuals who have beneficial mutations that say allow them to eat a specialized diet in the environment the organisms are in, or that produce a structure that might be beneficial to them like an eye. There's also balancing selection, which promotes variation or polymorphisms in a population. And lastly, there's genetic drift, which is the topic of this lecture today, of course, and is very intertwined with the concept of effective population size. I'll try to not use these concepts interchangeably because effective population size is quite a technical term that has a different meaning from genetic drift. But know that these two things are very related. Here I've denoted in red the evolutionary forces that either introduce new variation into a population or maintain variation. So just note that of all these evolutionary forces mutation and migration, if we're just looking at one population, migration into the population is going to add new variants to our population. And also balancing selection will promote or maintain genetic variation. But note that other types of natural selection and genetic drift actually lead to the loss of genetic variation in a population.