>> Let's talk a little it about heredity.
So the first topic I want to look at is nature and nurture.
And so you might remember that we looked at this
as a controversial issue in child development before.
Is it nature, or is it nurture?
Is it more of one?
Is it more of the other?
And pretty much the consensus has come,
as you might remember, that it's both.
And so we look at that through the epigenetic framework,
and the epigenetic framework basically says
that the expression of our genes can be affected
by the environment, and the environment can affect the
expression of our genes.
So when you think of genetic predispositions,
those things might not happen
if they aren't influenced by the environment.
So type 2 diabetes, for instance.
You may be genetically predisposed to develop diabetes,
but depending on your lifestyle
and your food choices will determine whether
or not you actually express type 2 diabetes.
And we also know that the environment can trigger certain
heredity conditions.
So, for instance, seizures can be triggered by a fever.
The fever doesn't cause the seizures.
It's not the reason behind the seizures.
Epilepsy is the reason behind that,
but that environmental trigger then allows
that expression of the disease.
So they're not separate.
They're very interrelated, and we look at that interrelation
with some different correlations.
So the first type is the passive-genotype-environment
correlation, and that essentially says that as long
as your parents are your biological parents,
you inherit both your genes
and your environment from your parents.
They give you both of those things, so those are going
to be kind of dovetailed because both of those come.
So in the picture there, you see an adult
and a child cross-country skiing.
So theoretically that parent could've passed on the gene
for that athletic activity to the child
but also would create the environment
that would allow those genes to be expressed.
Then you also have the evocative-genotype-environment
correlation.
And that refers to the fact that the social environment's going
to change based on the characteristics,
the inherited characteristics of the individuals in it.
So I chose this picture of the children kind
of in a social setting.
And you can see that some of them are interacting
with the mascot and kind of are embracing that situation
and would change that dynamic.
And you can see the little girl off to the left there
that looks a little bit more hesitant, a little bit more shy.
We also had the active-genotype-environment
correlation.
That essentially says that you are going to seek
out environments that match your genetic predisposition.
So if you are athletic --
maybe soccer skill runs in your family --
you're going to seek out other children in an environment
where you can play soccer.
We call that niche picking or niche picking.
And then the last one is the genotype-environment
interaction, and that essentially says that depending
on your genes, you may be more sensitive
to certain environmental factors than others.
So in the instance of pesticides,
you may be more genetically likely to develop cancer
from that exposure than someone else.
So there's all these different ways of looking
at how nature/nurture interact, but I think it's important
to note that heredity isn't the end-all, be-all.
It is that recipe, right?
It is kind of what's laid out, that if everything goes exactly
to a certain plan, you'll get a certain outcome.
But if you change that -- the way you prepare the food,
you know, you're not necessarily going to get the same thing
as you do if you would follow the recipe exactly.
So let's look at kind of the building blocks of heredity,
kind of where it comes from.
So within every cell is a nucleus,
and within that nucleus is the genetic material.
That genetic material is found on chromosomes.
And so those chromosomes are made up of coils of DNA,
and on those coils of DNA are our genes.
And our genes are what affect everything
that DNA controls, right?
It all goes down to the genes.
What genes do we have?
So there are two different ways that our cells replicate
and pass on our genetic information.
So with the exception of one type of cell in our body,
all of the rest of our cells use mitosis to divide.
And mitosis just means that they create a duplicate copy
of themselves.
Now, things can go wrong when we make that copy.
We can have mutations, but in general, that cell that results
from -- or two cells that result
from mitosis are exactly the same as the parent cell.
Now, the one cell that doesn't divide this way is our gametes,
right?
So if you are male, your sperm.
If you're a female, your ova or what we also refer to as eggs.
It's really important that those don't have all of the cells
because they have to combine to create an embryo, right?
So when your sperm and ova divide, they only pass on half
of their genetic information so that when that ova
and that sperm meet during conception,
then there's a complete copy of genetic material,
a complete version of genetic material.
And if you're wondering what human chromosomes look like,
here is an image.
So you can see 22 pairs of chromosomes.
And for the most part,
those chromosomes look really similar, right?
They kind of match one another, and that is essentially
because they have genes on each one of those chromosomes
that match one another.
And that's going to be important for what we're
about to talk about in a second.
And then down in the right-hand bottom corner,
you can see a pair of X chromosomes and a Y chromosome.
X -- if you have two X chromosomes,
as the pair there does, you are genetically female.
If you have one X and one Y,
which you can see the tiny little Y chromosome there
in the corner, that makes you male.
And then we'll look at what happens when you have more
or less of different chromosomes a little bit later
in this little mini lecture.
So some other key terms to be aware of when it comes
to inheritance are genotype and phenotype.
So a genotype is your genetic material, so that image
on that last slide, right?
This is the genes that you have, that if someone were to look
at your genes, this is what they would see genetically,
you know, your DNA profile.
But we don't express our genes the same way,
and sometimes we don't express something
that we have genetically because of the way it's passed on.
So what we actually see based on our genes is our phenotype,
the features that we actually express.
Now, whether or not we express something goes
down to patterns of inheritance.
And so for each type of gene --
remember you have two chromosomes, so you have a copy
of a gene on one chromosome and the other.
If those copies are the same, you hare homozygous.
So if you remember back to high school biology,
you might have done these Punnett squares here.
And you can see that in this instance the genetic --
the genes are either a capital Y or a lowercase y,
and they've also color coded them for us
to make it a little bit easier to see.
So if you have two copies of the lowercase y,
that green lowercase y, you are homozygous.
Or if you have two copies of this uppercase Y that happens
to be yellow, you are homozygous.
If you have two different copies of the genes,
so on one chromosome you have a uppercase
and on the other you have a lowercase,
that makes you heterozygous.
So you can see that here.
There's an uppercase Y and a lowercase Y,
and that's important because of the way we pass our genes
on and what we express.
So let's look at that on the next slide.
So there are two ways that are kind of simple to look
at that we inherit things.
So we have dominant and recessive.
And so if you -- if a trait is dominant, all you have
to have is one copy of the gene in order to express that trait.
So things like dimples and curly hair
and dark-colored hair happen to be dominant.
So if you get one of those copies of the genes
from either parent, you're going to show
that characteristic or trait.
On the other hand, you have recessive.
Recessive means that you need to have both copies of that gene
in order to express it.
And so you had to get it from both of your genetic parents
or your biological parents.
So those happen to be things like having red hair
or being nearsighted or having straight hair.
Those are less likely to happen because you have
to get both copies of the genes.
Now, most things aren't that simple.
It's not just a matter of one pair of genes that we have
to look at, so those things we refer
to as having a polygenic pattern of inheritance.
There's multiple genes that all intertwine
to affect how a trait is expressed.
Eye color is one of those things.
We used to think that it was kind
of a dominant/recessive type of inheritance, but now we know
that it's actually more complex than that.
So many things are actually polygenic.
So what happens when heredity doesn't quite go right?
So with genetic and chromosomal disorders.
So we've got five different types of disorders.
Three are related to kind of genes in general.
Two happen to do with the number of chromosomes you have.
So let's take a brief look at each of those.
So some dominant disorders include Huntington's disease,
Tourette syndrome, and achondroplasia,
which you can see in the image there.
Recessive disorders include things like sickle cell disease,
cystic fibrosis, PKU, Tay-Sachs, and albinism,
which you can see in the image.
And then we have sex-linked disorders, and those are --
happen more often in males
because there's only one X chromosome,
and we know the Y chromosome, if you remember back
to that picture, is much smaller than the X chromosome.
So if a gene happens to show up on that X chromosome,
it's more likely to be expressed because there's nothing
to offset it in the Y chromosome.
So sex-linked disorders include fragile X syndrome, hemophilia,
and Duchenne muscular dystrophy,
which you can see in the image there.
And as I mentioned, chromosomal disorders happen
when you have too few or too many chromosomes,
so some general chromosomal disorders tend to be
when there's extra copies of a chromosome.
So those include Down syndrome, which is trisomy 21.
Trisomy 9, mosaicism.
Mosaicism just means that it's not every cell,
so it could be anything to a few cells to a majority
of the cells, and the severity
of that particular disorder depends
on how many cells are affected.
We also have trisomy 13 and trisomy 18.
The little boy there in the image happens
to have trisomy 9, mosaicism.
And then the last are sex-linked chromosomal disorders,
and so this is when that 23rd pair has an issue, right?
So the other 22 pairs we're not worried about.
It's the sex chromosomes.
So if you are missing an X chromosome,
you can have Turner syndrome.
If you are male, and you have an extra X chromosome,
you could have -- you'll have Klinefelter syndrome.
If you have an extra Y chromosome,
that's called XYY syndrome.
And if you're female, and you have an extra copy
of your X chromosome, such as the young lady on the end there,
that's called triple X syndrome.
So I hope this video helps you understand heredity a little
bit more.
It is complex, but you don't have to know all
of the really deep, deep details.
Just kind of have a basic understanding of how it works.