Regulatory genes | Behavior | MCAT | Khan Academy


OK, so as scientists and
as psychologists study gene and environment
interaction, they’re really beginning
to get as specific as identifying the
particular genes which are regulating our behavior. And this gives rise
to an entire new field of science called
molecular genetics. And molecular
genetics as a field is a science that looks at
the actual molecular structure and the function of genes. So we’re actually looking
at the segments of DNA. And it was actually
around the 1950s that James Watson
and Francis Crick helped discover the structure
of DNA, which gave rise to really a whole lot of
brilliant discoveries. And one such discovery by
Crick, by Francis Crick, gave rise to what we
call the central dogma of molecular genetics. And the central dogma
of molecular genetics essentially just says
that segments of DNA called genes– so
a segment of DNA called a gene– codes for
RNA or ribonucleic acid. And the little
units of RNA called codons are going to code for
one of the 20 amino acids. So this is an amino acid. And at this point, it’s
becoming a little bit more of a biology concept. But these amino acids that
are being coded for eventually become the building
block of proteins. And it’s these proteins
that are being created that actually
function in our body. So think of enzymes,
which are proteins that speed up
reactions in our body. Or you can think of the proteins
that determine whether or not a substance can cross
the different membranes inside of a cell and on
the outside of a cell. And there are many different
types of proteins in our body. But the point is
that proteins kind of form the intermediate point
between genes and our behavior. And I’m using the
word “behavior” because in psychology
that gives us a really nice, broad reference
to our body’s functioning and our response
to the environment. So the central dogma
of molecular genetics really puts a heavy
emphasis on the role of DNA in really determining all the
outcomes of these proteins that cause our behavior. But actually subsequent
discoveries, especially those in this
molecular realm, have caused us to reconsider the
relative importance of DNA sequence– so our
gene sequence– in determining the function. So as an example, think about
steroids, which are hormones. And you can think of that
as an environmental factor. And so you can think of
the steroid testosterone. And so we’ve heard that steroids
travel between different parts of our body to elicit responses. But those responses are
actually the activation of genes to produce proteins. And if we want an example
that’s even more environmental, we can think of a stimulus
outside of our body like pheromones. And pheromones really
do the same thing because they’re
exciting the brain and they’re causing a
response inside of us. But that response
again essentially is the turning on of genes
to make these proteins that are going to form a
function in our body. But if you think about
it, in both of these cases the central dogma is kind
of being flipped over because where at
one point we put a really heavy deterministic
emphasis on the DNA structure– so the gene structure– in
determining the protein that causes our behavior,
now we’re actually shifting that
determinism outside of the DNA sequence
a little bit. So these phenomena are
going to introduce us to the idea of gene regulation. And this idea of gene
regulation becomes really important to our
discussion of environment, and heredity, and behavior. So there’s kind of
this entire modulatory world to genetic expression. And I say modulatory
because the gene expression is being modulated by
an environmental factor. But one of the
greatest achievements in clarifying these
modulatory factors has been the mapping
of the human genome. And so in the last two
decades, scientists have mapped our
entire genome, which accounts for like
30,000 or so genes. And so here in the
background, I’ve kind of drawn an example
of this mapping with all 46 of our chromosomes. And we can see that these
might be the genes here. And scientists
have mapped out all of the genes that
contribute to our genome. And so while in
recent history, we’ve relied heavily on twin
and adoption studies to narrow down the heritability
of behavioral traits, now that we mapped the
entire human genome, we can look at populations
which share traits and essentially
look at the genes that we expect to be
contributing to those traits. And we can compare and
contrast those genes. And these studies have given us
some really, really fascinating results. As an example, we’ve discovered
that the vast majority of our genes– I think on the
order of 95% or so of our genes don’t actually
code for proteins. But rather, they regulate
how those proteins are coded. So instead of changing
the protein, they actually change the context
of the protein and when and how it’s
expressed, so kind of like little if-then statements. If we experience
sugar consumption, then we code for the
protein hormone insulin. And there’s this whole
playlist in the biology section that covers gene
control and covers this modulatory world
of gene expression. So I’m not going to
go too deep into it. But it is an important point,
especially as we actually see differences in the molecular
structure of genes contributing to the heritability
of our behaviors. And then even outside of the
study of the DNA structure and the gene sequence,
we’ve started discovering other things at
this molecular level that are affecting gene expression. And this is an entire
new field now concerned with this called epigenetics. And so epigenetics is
the study of the changes in gene expression resulting
from changes to something other than the DNA sequence. And a classic example
of epigenetic influence is methylation, so the addition
of methyl groups to the gene. And the addition of
these methyl groups can actually make it more
difficult for the transcription factors to come in and
identify and activate the gene. So the gene essentially
isn’t expressed, not because the
sequence is irritated. But rather because something
is inhibiting the activation. And we actually see
this phenomenon in rats. So different styles
of rat mothering can nearly permanently
change the stress response in our offspring
due to methylation. So we see our environment
causing this methylation, which affects gene expression. And so in a sense,
these epigenetic factors are capable of overriding
the DNA sequence in determining our behavior. And so these ideas
are quite biological compared to the
majority of psychology. But molecular genetics
and epigenetics really represent the next
step in sorting out the heritability
of our behavior.

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