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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.
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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.
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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.
