Now, let’s get into
Genetics, hereditary genes,
these are all things that have been
coming up in lot of our modules.
And right now we’re going
to break this down into the
main components that make
up behavioral genetics.
So first we’ll get in some
basic nomenclature, genotype.
So genotype of an organism is the inherited
map it contains within its genetic code.
So that’s the genetic
The phenotype is the observable
characteristic and traits of that organism.
So having blue eyes or brown
hair or a certain color of skin,
that would be the
but what’s mediating that and what’s
controlling that and what’s causing that
to be expressed would be the genetic
information or that person’s genotype.
examines how genotype and
the environment affect
our expressed phenotype.
So just because you’re wired to
have a certain genetic trait,
so genetically, on the blueprint
it says you should have this,
it doesn’t necessarily mean you’re
going to actually express that,
and that’s because of the impact
that the environment can have.
So heredity is the passing of traits
from the parents to the children,
so eye color, hair
color, that’s passed on.
We’ve also talked about
things like certain behaviors
or certain disorders or
being prone to certain
That means you have the genetic
-- you have the genotype
to potentially, say, get depression because
we’ve shown a hereditary linkage between
parents and children when we’re
talking about this disease,
and that’s through the passing
of this genetic information.
Traits or attributes can
include things like eye color,
hair color, shape of face,
which we’ve discussed,
and individual traits are
encoded in this DNA.
if we’re looking at
the actual process,
and again, we don’t need to memorize
all of these various steps,
but what we’re saying is we have the
genetic information found in chromosomes
and that goes on to then go through the
process of transcription and expression
and we get expressed behaviors, and this
is all linked back to the actual DNA.
So we can go in and look at specific
strands of DNA, understand the sequence,
and that gives you a good a map
of exactly what controls what.
So we’ll look at
that in just a sec.
So genes and environment work together to
influence our state, active versus inactive.
So a gene, just because
it’s there it doesn’t
mean that it’s actually
going to express itself,
it needs to be activated,
or it can be inactivated.
So we know that the
environment can actually have
a huge role in activating
and inactivating genes.
So we say the environment can
mediate level of chronic
stress and can activate or
inactivate specific genes.
So let’s use an example, you’re
a modestly healthy person,
life is good, you have no
disorders, everything is great,
and all of a sudden you start
studying for the MCAT,
it’s kind of stressful, you get in
medical school, kind of stressful,
you become a well-renowned
surgeon, extremely stressful.
Being in the stressful
environment will actually
modulate and change
expression of specific genes.
And we’ve shown that this
chronic exposure to stress
will then go on to activate
or inactivate these genes
depending on what it is that they
do and depending on what effect
those environmental stressors
are having one you,
and this can then go on to lead to
behavioral or phenotypic changes.
So great example of how the environment
is impacting expression of your genes
which goes on to change the expression
of a behavior or your phenotype.
Now, temperament is something that’s unique
and it’s sort of how we express ourselves.
It refers to the emotional excitability and
aspects of an individual’s personality.
So you can have different
types of temperament
and you hear people say what’s their
demeanor or what’s their temperament like,
or that person has quite a temper, and
that’s what they’re referring to.
So now, is this something that you’re born
with, is this something that you develop?
It’s kind of a combination of both, but
initially, there’s a large innate,
innate or from within at birth portion
and there’s some of it that’s learned,
but your basic temperament typically comes
from innate behaviors or it’s innately set.
So temperament also focuses
on behavioral profiles that
are easily measurable and
testable in early childhood.
So as a child,
I can say this baby has
this type of temperament.
And I think to keep it simple,
what we’ve done is we’ve put
it into two broad categories.
So you can have two
main types of babies.
The first being an easy baby, and
this is a baby that’s fairly relaxed,
easygoing, likes to play a lot,
smiles, it’s quite engaged.
There are ones that have good
eating and sleeping schedules
There are ones that have good
eating and sleeping schedules
and those of you who have young children
always pray, “Please let me have
an easy baby and not have a baby that’s
whining and crying all the time.”
So this baby is one that you can
put down anywhere, they’re happy.
You can pass them to
anybody, they’re happy.
You can put them to bed at three, at six,
at nine and it almost doesn’t matter.
They’ll sleep any time, they’ll eat
anything, they’ll eat quite easily.
These are easy
babies, the dream.
Now, the opposite is a
difficult baby, still cute,
but sometimes you maybe want to
strangle them a little bit, right?
And they’re highly irritable, easily
upset, always crying and whining,
and I’m not talking about like a toddler,
I’m talking about a newborn baby.
You try to put them on a schedule,
you try to have them sleep,
feed, eat, and that’s
very, very difficult.
So, thus, the names easy
baby, difficult baby.
Now, let’s take a look
at the adaptive roles
of traits and behaviors
and how these change.
Okay, so we’re going to look at a range of
two types of behaviors, innate and learned.
So these are ones that you’re born with and
these are ones that you learn over time.
They’re more adaptive in nature.
So in the innate ones you have ones that
are genetically programmed behaviors,
inherited or they’re intrinsic or
stereotypic, inflexible; versus adaptive.
These are ones that are not inherited,
that are extrinsic, permutable.
They can change,
some of the innate ones
are things like reflex,
and we talked about
that knee jerk reflex,
orientation is how you orient
something called fixed
So an example would be, say,
I’m thinking animal kingdom,
a frog trying to catch a fly or the praying
mantis that is trying to attack its prey.
Once it initiates that response, which
usually involves a couple of movements,
it really can’t stop that.
It’s a fixed action pattern, it’s fixed,
it’s going to go and do its thing,
So once that frog has got its
tongue out trying to catch a fly,
that’s it, it’s gone, right?
And same thing with
the praying mantis.
Once it’s going to do its
strike to hit something,
that’s it, it’s a
go ahead movement.
It’s not really thinking about
it and you just follow through.
As humans, we have, you
know, a lot of similar
things where there are
movements or behaviors
that we do where once
you kind of just you go
through, you follow through.
Now, in reality, we know that it’s never
really just purely innate or just learned.
We have a nice mix of a lot of
what we do is actually complex.
So it’s a combination
of the both
and it’s done to allow us to
maintain a certain consistency.
And so one of that
consistencies we’re trying
to maintain is something
It refers to the body’s drive to
maintain a consistent internal state.
So a certain temperature,
a certain blood pressure,
and you need to modify your behaviors
in order to maintain that homeostasis.
So, some of the behavior
modification can be done through
this combination of innate
and learned behaviors.
this modulation of behavior
is called adaptation,
and we do this adaptation to
maintain our homeostasis.
So there’s a range of observable
behaviors based on these categories.
let’s take a look at
how we figure out
what impacts -- what a lot
of things are happening,
whether it’s behavior or whether
it’s a certain medicine
or if we’re looking
at a certain trait
and we want to look at
what impact that’s having.
One of the easiest ways
we’ve been doing this
over the years is looking
at twin studies.
So twin studies allow
us to examine the
heritability and environment.
So two main factors that
normally will drive a
change or expression in
the phenotype or behavior
are -- well, did you get from your genes
or is this impact of the environment?
So we have two types of twins.
Monozygotic or identical twins and they
have essentially the exact same genotypes.
So what we’re doing by looking at these
individuals is that we’re removing
heritability out of the
equation because the idea is
if they have the same
you know, if one was being inherited,
it should be with the other.
So now we can look at if
it was expressed or not,
and that expression was going
to be more prominently due to
environment because we’ve removed
genetics out of the equation.
And there’s dizygotic or
fraternal twins and this
is where they share roughly
half of their DNA.
So here, the linkage
isn’t as direct,
but it’s still better than or is
comparable to the general population.
So heritability estimates the
variation in a trait that is
due to genetic variability
and is population dependent.
So if you’re in the general population, you
would have a certain level of expression
versus if it was in your genes, you would
have an elevated level of expression.
So it’s also influenced
by environment, so shared
So you can have two twins that are
monozygotic, so identical twins,
and you separate them by birth
and they live separate lives across
the globe with two different --
two different families,
schools, friends, everything.
We will find that a lot of
behaviors and certain traits
will be identical even though they have
completely different environments,
but then will also have certain traits
that are environmentally driven.
So it’s a combination of both.
So heritability does not pertain
to an individual, but rather to
how two individuals differ, and
that’s a really important point.
the heritability is not saying something
specific about that young girl,
but it is going to allow us to say something
that’s different between her twin sister
or her and a comparable that’s
in the general population.
So an example is IQ.
So if we say, you know,
she has a certain IQ,
I’m not saying that the
heritability is influencing her IQ,
it’s influencing or it’s allowing us to
better understand the difference in IQ.
So it’s kind of an important
point that you got to grasp.
So let’s take a look at the role that
the environment can play on genetics.
So genetics can be influenced by both
the predisposition and the environment,
so we’ve mentioned that before.
You’re born with you genes and
that’s part of the equation,
but the environment can
influence expression of genes.
So a good baby versus a
difficult baby and the
This is a great example
of genes and environment.
So take a look at this
scenario, you have two babies.
We have the first baby,
which is the good baby,
and this baby is amazing.
The baby sleeps
great, eats great,
you know, it can pee or poo on demand,
perfect and incredible child,
and as a result, how do
you treat that child?
You’re like, “Oh, you know, my
little Timmy, he’s an angel.
He sleeps great, he’s such a
cutie pie, he never cries
and everybody comes around
to check our little Timmy
and they’ll gather around little Timmy.
Oh, he is so cute.
Look at him smile and
he smiled at me.
And will he let me hold him?
Oh my God, he will.
I think he -- what a nice kid. He’s such
a sweetheart, oh my God, oh my God.”
This continues, and let’s
just roll this out.
As he continues to be a good
baby, he becomes a good toddler,
always eats his food, sleeps on
time, doesn’t argue, doesn’t cry.
He can be playing with
other kids, plays well.
All of a sudden, people
continued around him to
say his mom, his dad,
visitors, family, friends,
“What a great baby. He’s
such an amazing baby.”
Now all this positive
reinforcement is creating a
pretty positive environment
around that child,
versus our devil baby, the difficult baby
who’s not eating, who’s not sleeping,
who’s always crying, is very,
very difficult to handle.
You know, people come over and they’re
like, “Oh, can I see little Timmy?”
And Timmy starts wailing
and kicking and screaming.
They’re like, “Well, maybe I’ll
just put him down and whatever,”
and you kind of internally will have this
perception that what a difficult baby and
you know, you know little Timmy is always
crying, and so they get negative feedback.
So now two different babies,
potentially the exact same,
you know, parents and interactions, but
how those interactions are played out
and the result in environment
around that child changes.
Happy baby, good baby,
crying baby, devil baby,
So that feedback that that baby
gets as they grow and develop
will directly influence how
they express their behavior.
So it’s pretty cool that, you know,
the environment that you create
will really have a result and effect
on the the ultimate behavior.
So, reciprocal relationship in that
environment can lead to genetic variation.
So if we’re looking at a
we see a reinforcement
of genetic expression,
and if you see a
you might see a change in
that genetic expression.