- [Voiceover] Before we go in-depth on meiosis,
I want to do a very high level overview
comparing mitosis to meiosis.
So, in mitosis, this is all a review,
if you've watched the mitosis video,
in mitosis, we start with a cell,
that has a diploid number of chromosomes.
I'll just write 2n to show it has a diploid number.
For human beings, this would be 46 chromosomes.
46 for humans, you get 23 chromosomes from your mother,
23 chromosomes from your father or you can say
you have 23 homologous pairs, which leads to 46 chromosomes.
Now after the process of mitosis happens
and you have your cytokinesis and all the rest,
you end up with two cells that each
have the same genetic information as the original.
So you now have two cells
that each have the diploid number of chromosomes.
So, 2n and 2n.
And now each of these cells
are just like this cell was,
it can go through interphase again.
It grows and it can replicate its DNA
and centrosomes and grow some more
then each of these can go through mitosis again.
And this is actually how
most of the cells in your body grow.
This is how you turn from a single cell organism into you,
or for the most part, into you.
So that is mitosis.
It's a cycle.
After each of these things go through mitosis,
they can then go through
the entire cell cycle again.
Let me write this a little bit neater.
Mitosis, that s was a little bit hard to read.
Now what happens in meiosis?
What happens in meiosis?
I'll do that over here.
In meiosis, something slightly different happens
and it happens in two phases.
You will start with a cell
that has a diploid number of chromosomes.
So you will start with a cell
that has a diploid number of chromosomes.
And in it's interphase, it also replicates its DNA.
And then it goes through something called Meiosis One.
And in Meiosis One,
what you end up with is two cells
that now have haploid number of chromosomes.
So you end up with two cells,
You now have two cells that each have a
haploid number of chromosomes.
So you have n and you have n.
So if we're talking about human beings,
you have 46 chromosomes here,
and now you have 23 chromosomes in this nucleus.
And now you have 23 in this nucleus.
But you're still not done.
Then each of these will go through a phase,
which I'll talk about in a second, which is
very similar to mitosis, which will
duplicate this entire cell into two.
So actually, let me do it like this.
So now, this one,
you're going to have four cells
that each have the haploid number
that each have the haploid number of chromosomes.
And they don't all necessarily have the same
genetic informatioin anymore.
Because as we go through this first phase,
right over here of meiosis, and this first phase
here you go from diploid to haploid, right over here,
this is called Meiosis One.
Meiosis One,
you're essentially splitting the homologous pairs
and so this one might get some of the
ones that you originally got from your father,
and some that you originally got from your mother,
some that you originally got from your father,
some that you originally got from your mother,
they split randomly, but each homogolous pair
gets split up.
And then in this phase, Meiosis Two,
so this phase right over here is called Meiosis Two,
it's very similar
to mitosis, except your now dealing with cells that start off
with the haploid number.
It's important to realize that meiosis is not a cycle.
These cells that you have over here, these are gametes.
This are sex cells.
These are gametes.
This can now be used in fertilization.
If we're talking about, if you're male, this is happening
in your testes, and these are going to be sperm cells
If you are female, this is happening in your ovaries
and these are going to be egg cells.
If you a tree, this could be pollen or it could be an ovul.
But these are used for fertilization.
These will fuse together in sexual reproduction
to get to a fertilized egg, which then can undergo
mitosis to create an entirely new organism.
So not a cycle here,
although these will find sex cells
from another organism and fuse with them
and those can turn into another organism.
And I guess the whole circle of life starts again.
But it's not the case with mitosis where this can keep
going and going, going.
This cell is just like this cell, while these sex cells
are differeent than this one right over here.
Now, where does this happen in the body?
We've talked about this in previous videos.
These are your somatic cells right over here.
These are the ones that make up the bulk of your body,
somatic cells.
And where is this happening?
Well, this is happening in germ cells,
As we mentioned, if you're male it's in your tesis
and if you're female it's in your ovaries.
And germ cells actually can undergo mitosis
to produce other germ cells that have a diploid
number of chromosomes, or they can undergo
meiosis in order to produce sperm or egg cells
in order to produce gametes.