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Hello and welcome.
My name is Joseph Blelawski.
I'm an evolutionary biologist.
I'm cross-appointed in the
Department of Biology and
the Department of
Mathematics and Statistics
at Dalhousie
University in Canada.
Today, I'm going to lecture on
an introduction to
and a comparison
of the neutral and
nearly neutral theories
of molecular evolution.
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Before we dive into the
details of those theories,
we need to do a quick review of
the three fundamental
processes of evolution.
They are genetic mutation,
natural selection, and drift.
Here I'm going to
start with mutation.
I've got a picture of the
familiar double helix
of DNA on the screen here,
which is the hereditary
material in humans
and almost all living organisms.
This is an information
storage system.
It's a biochemical
system in a language
that has an alphabet
of just four letters.
Not unlike our language
with 26 letters,
but much more efficient.
The information
stored in the DNA
is determinant of a
heritable phenotype.
I need to be careful here.
I do not mean full
genetic determinism.
It's important to remember
that the environment
can also affect phenotype.
These phenotypic effects
of the environment
are not transmittable
from parent to offspring.
Just a quick example.
Imagine an organism loses
a limb at some point.
It's not going to transmit
that loss of limb
to its offspring.
When we talk about
the genes or the
genetic information being
determinants of phenotype,
we're saying it's the
fraction of total phenotypic
variation that can
be transmitted from
parents to offspring over time.
We talk about the unit
of that transmission of
information between parents
and offspring as a gene,
which brings us to mutation.
Mutations are thought about
in the context of genes,
and they are the
ultimate source of
heritable phenotypic variation
that is subject to
evolution over time.
