Purpose of Meiosis and Fertilization (2023)

Introduction

This is a broad overview about what meiosis does and why it's necessary in order for offspring to be created.

#meiosis #sperm #ovum #gametes #zygote #fertilization #apbio

Content

How are genes passed down from Mom and Dad because that's where those genes come from from Mom and from Dad here's a cartoon, a drawing of that karyotype right? That shows all 23 Pairs and each one is in a pair right, so chromosome 9, for instance, there's two there chromosome 16, there's two! Each chromosome is actually a pair.

You have a pair of them and one set comes from Mom and the other set comes from Dad, and that's why there are two of each chromosome, so you can kind of think of it as like.

You know your shoes, you have a left, shoe and a right shoe and if you have 23 pairs of shoes well, maybe all the left shoes came from Mom and all the right shoes came from Dad.

You have 23 pairs of shoes here or 23 pairs of chromosomes, but you actually have 46 total shoes or 46 total chromosomes.

So half of the chromosomes come from Mom and half of the chromosomes come from Dad and more specifically, one of each chromosome comes from Mom or from Dad.

So where do these chromosomes come from? How are they delivered to you? Well, Mom and Dad.

Both have cells inside their body that are called germ cells now I know you're, thinking like germs, yeah, like a bacteria or fungi, or things like that right.

No, this, this germ cell, those are germs, but when we talk about the germ cells found in Mom or Dad, we're talking about these specific cells that have the ability to undergo meiosis, okay and these germ cells go through the process of meiosis to become sperm in dead or eggs in Mom, okay, so the germ cells are the only cells that can go through meiosis to form sperm or eggs.

Now we're talking about humans here right with sperm and eggs, but really any organism that undergoes sexual reproduction has some form of this process of passing along uh chromosomes and DNA to the Next Generation, whether it's plants or animals humans.

They any organism that undergoes sexual reproduction has some form of this process.

So these germ cells have two of each chromosome, because you know Mom and Dad are human, so all of their cells have a pair of chromosomes and The.

Germ cells have a pair of chromosomes too.

So in this case I'm only showing you one pair.

Maybe this is chromosome one and dad and mom both have a pair of chromosome one, but keep in mind in those germ cells there'd be 23 pairs, because that's what Mom and Dad have is 23 pairs of chromosomes.

So meiosis, though, is going to split those chromosomes.

It's going to separate the pair so that in the sperm there's only going to be one of each chromosome and the same thing for the egg, there's only going to be one of each chromosome in the egg, so just 23 not two sets of 23, but just one set of 23 and that's important, if you think about it, because that sperm is going to fertilize the egg and that fertilized egg is the first cell that becomes a new individual.

So the sperm is going to contribute one set of 23 chromosomes to this human and the egg is going to contribute the other set and together that's going to have two of each chromosome or 46 total chromosomes and that's what it is to be human is to have two of each chromosome and to have 23 pairs or 46 total chromosomes.

We call the sperm or the eggs gametes and just as a side note, sometimes you'll hear spermatazzoa and that's the same term as sperm and for eggs, mom's, eggs, they're called OVA right and a singular egg.

One egg is known as an ovum, so you might also hear those terms for Mom's eggs, but the sperm and the eggs.

Those are the gametes, so germ cells undergo meiosis to form gametes and in dad that's going to be sperm in Mom, that's going to be eggs.

Now these germ cells are found in the testes of men.

That's where meiosis of those germ cells takes place to form the sperm, which are also found in the testes in mom those germ cells undergo meiosis in the ovaries to form the eggs.

So, in the process of fertilization we have a sperm that's going to enter an egg and the sperm is bringing one set, of 23 chromosomes.

The egg has the other set, of 23 chromosomes.

So, together that fertilized egg has two sets right of 23 chromosomes.

It has a pair of each chromosome for a total of 46 chromosomes.

Now that fertilized egg is also known as a zygote, so scientifically when sperm enters egg.

When fertilization occurs now we have a zygote.

So here's the filling question for you just to see if you can bring all this terminology together, pause the video and see if you can fill in words in the four blanks that are found here.

Okay pause: the video okay: did you pause the video all right? Well, let's talk about this and and see if we can fill in the different terminology here: okay, blank undergo meiosis to produce blank in men and blank in women.

Okay germ cells, are the things that undergo meiosis and those germ cells.

Are going to differentiate or become sperm in men? And OVA or eggs in women? Just as a reminder, here's that diagram we use where the germ cells and Dad are going to undergo meiosis to form the sperm and The Germ cells in Mom's ovaries are going to undergo meiosis to form her eggs, her OVA now here's the second sentence when fertilization occurs.

So when a sperm enters an egg, a blank is formed.

In this case it's a zygote right, a fertilized egg, which is scientifically known as a zygote and here's the process right.

We have two different kinds of gametes: there's sperm and egg.

So when sperm enters egg in the process of fertilization, a zygote is formed and that zygote now has the full set of chromosomes 23 from Mom and 23 from Dad.

So here's another graphic just to sort of remind you that there are 23 individual chromosomes coming from Dad and is going to be found in Dad's sperm and there are 23 individual chromosomes that are coming from Mom in her egg and so when the sperm fertilizes, the egg.

We end up with that zygote that fertilized egg that now has two of each chromosome.

So the process of meiosis is really important, because if those chromosomes didn't get separated for each pair, then when fertilization occurs, there would be four of each chromosome inside that fertilized egg and that's not conducive to life.

That's not going to cause a cell that you know becomes an individual there's, some terminology we use to talk about the gametes, the sperm or the egg or the other cells in our body and the gametes are known as as haploid.

Okay.

Haploid is a term that we use to indicate that that cell has one of each chromosome, not two okay, so the sperm and the Egg only have one of each chromosome they're haploid.

All other cells in the body are known as diploid, and you can remember that, because dye means two so diploid cells have two of each chromosome and here's an easy rule to remember in humans, all cells of the body are diploid, except for the sperm or the Egg, except for the gametes.

Okay, the gametes are haploid, so all cells in your body are diploid.

They have two of each chromosome, except for the sperm and egg which are haploid.

They only have one of each chromosome.