Okay. Let’s take a look at the
influence of genetic and environmental
factors and how that shapes the
development of our behavior.
So we know that behavior is shaped by individual
experiences and our social experiences
and development of one’s behavior is
shaped by a couple of key factors.
One, we’ve already mentioned, is biology.
So what are the genes?
The genetic information passed on to you is
going to be a huge driver of your behavior.
The second is actually
so before you’re even coming
out to the world to say hello,
while you’re in your mother’s
womb the environment there,
the conditions there, the conditions
that impact your development
will have a huge role, and
in physiology, as well.
Now, let’s talk about the brain.
Psychology, psychologically speaking,
the gene environment interactions, prior
experiences, beliefs, feelings, culture --
sorry, not culture. These things
will really impact your psychology.
What is the psychological support that
you have? What’s the support network?
These things will all
really play a huge role
in relation to our third point of
societal and cultural factors.
Do you have family? Do you have friends,
the people you can get help from?
What are the cultural
norms around behavior?
That will really have a huge impact on how
you interact with the world around you.
So all these different things can
really, really impact and change
the development of
Now, let’s take a look at the
role of genes in behavior.
So molecular biology is the study
of molecular underpinnings
of the process of replication, transcription,
translation, and cell function.
So in your genetics module that you’re
going to have to do prepping for the MCAT,
you’re going to go through
all of this process.
So what I want you to understand
is there is a process where
DNA ultimately gets
converted into proteins,
and throughout that process
of protein expression,
that can have a huge
impact on actual behavior.
So now we’re linking biology, good old
biology to actual psychological changes
and output in societal behavior.
So Central Dogma of molecular
biology is an explanation of the
flow of genetic information
within a biological system.
So we say that DNA makes RNA,
and RNA makes protein,
and this makes --
sorry, and the protein
expression can impact behavior.
So it’s kind of a neat idea.
So DNA, which is encoded in you,
through different processes
makes RNA, which makes protein,
and levels of protein expression
will affect your ultimate behavior.
So when we’re causing a change
in behavior, we’re actually
getting right down to the level
of protein expression, okay?
So that’s a really cool way to look at it.
So we’re going to look at sort of
regulatory genes and behavior.
So we have DNA through the
process of replication,
and we’re not going to get into
a whole genetics discussion,
but we go on to transcribe RNA, and
then we go on to create protein.
Now, different levels of protein expression
like I say will affect behavior.
Now how is protein expression controlled?
Well, it all goes back
down to regulatory genes.
So the human genome is
made up of 23 chromosomes.
So this has all been mapped out.
So for the human genome we have mapped
out all the different chromosomes
and what it is that they do.
So, a couple of really interesting things.
Protein-coding sequences account for
only 1.5% of the entire genome.
So out of the whole genome, only
a very, very small fraction
is really influencing
So vast quantities of non-coding
DNA within the genome
are associated with biochemical
activities including gene regulation,
so the bulk of the genes, a bulk of
the DNA is doing something else.
A gene regulation can
modulate the expression
of a protein versus
So what we’re saying is the bulk of
protein is normally coded by that 1.5%,
and if you go on and activate and inactivate
and modulate or modify the other genes,
that can go on to
So you’re using sort of an indirect
means to influence protein.
So the direct effects of these changes
and changes in protein
expression will impact behavior.
So epigenetics is the
study trait variation
caused by external environmental
factors that switch genes on and off.
So this is a burgeoning area of study now
because people are really, really interested
in understanding well, what is
actually impacting my behavior?
What in the environment, what around me
is going to activate or
inactivate certain genes?
So study of how cells
read DNA instead of being
caused by changes in
DNA sequence, okay?
So processes like methylation
or histone modification
alter how genes are expressed
without changing the DNA sequence.
So we’re not actually changing
the sequence of your DNA,
we’re just changing
sort of the on and off.
So you should be familiar with the fact
that methylation or histone modification
refers to the fact we’re
turning gene expression, okay?
So that’s the on and off versus actually
changing the DNA sequence, okay?
So we got some figures and some
analogies, this might help you.
So if a gene is switched on, we have active
chromatin, and that means it’s open.
And unmethylated cytosines,
and we’ll have a diagram,
those are the ones with circles,
they’re still there, and we
have acetylated histones.
Now on the off side, it’s silent.
We have condensed chromatin, the methylated
cytosines, which are red circles,
and we have a deacetylated histones,
that would be the off switch, okay?
So here in this diagram you
can see the little circles
represent the histones
and the methylation.
So on the top transcription is possible,
and so we have normal DNA production
and protein production
with RNA transcription,
and on the bottom one we can see
that transcription can be impeded
and now you actually can’t just transcribe,
you can’t cause the protein expression.
So one is an on, and one is an off.
And so based on the
you can be in one of
these states, in an on
state if you’re normally
on a resting state,
or it might be the opposite, you
might be turning an on gene off
and, again, that will impact the
level of protein expression.