Comparing mitosis and meiosis | Cells | MCAT | Khan Academy

Summary

This video script provides a clear comparison between mitosis and meiosis. Mitosis involves a cell with a diploid number of chromosomes (2n), duplicating its DNA and dividing into two identical cells, both with 2n chromosomes, which can repeat the cycle. In contrast, meiosis starts with a diploid cell, undergoes DNA replication, and then splits into two haploid cells (n), each with half the genetic information. These cells further divide into four haploid gametes, which are crucial for sexual reproduction and fertilization, unlike the continuous cycle of mitosis.

Takeaways

• 🔬 Mitosis starts with a cell having a diploid number of chromosomes (2n), such as 46 chromosomes in humans.
• 🌱 During mitosis, the cell replicates its DNA and undergoes cytokinesis, resulting in two identical cells with the same genetic information.
• 🔄 Mitosis is a continuous cycle where the resulting cells can enter the cell cycle again, allowing for growth and development.
• 🧬 Meiosis begins similarly with a cell containing a diploid number of chromosomes, but it proceeds in two distinct phases.
• 🧬 Meiosis I reduces the chromosome number from diploid (2n) to haploid (n), creating two cells with half the genetic material.
• 🌟 Each cell from Meiosis I then undergoes Meiosis II, similar to mitosis, but starting with haploid cells.
• 🌈 The result of Meiosis II is four haploid cells, each with a unique combination of chromosomes due to the separation of homologous pairs.
• 🌱 Meiosis is not a cycle; the cells produced are gametes (sperm or egg cells) used in sexual reproduction.
• 🌳 In humans, meiosis occurs in the testes for sperm cells and in the ovaries for egg cells.
• 🌿 Germ cells can undergo mitosis to produce more germ cells with a diploid number of chromosomes or meiosis to produce gametes.
• 🌐 Meiosis plays a crucial role in sexual reproduction, as the haploid gametes from two organisms fuse to form a fertilized egg, initiating a new organism.

Q & A

What is the starting point for both mitosis and meiosis in terms of chromosome number?

Both mitosis and meiosis start with a cell containing a diploid number of chromosomes, denoted as 2n. For humans, this means starting with 46 chromosomes.

What is the outcome of mitosis in terms of the genetic information of the resulting cells?

After mitosis, the two resulting cells each have the same genetic information as the original cell, maintaining the diploid number of chromosomes (2n).

How does the process of mitosis contribute to the growth of an organism?

Mitosis contributes to the growth of an organism by allowing cells to divide and produce two identical daughter cells, which can then enter the cell cycle again, thus facilitating the development from a single cell to a multicellular organism.

What is the main difference between the starting point of meiosis and mitosis?

While both processes start with a diploid cell, meiosis involves two distinct phases and results in cells with a haploid number of chromosomes (n), unlike mitosis which maintains the diploid state.

What occurs during Meiosis One that is different from mitosis?

During Meiosis One, cells undergo a process that results in two cells each having a haploid number of chromosomes (n), which involves the splitting of homologous pairs and the random distribution of maternal and paternal chromosomes.

What is the purpose of Meiosis Two in the context of cell division?

Meiosis Two is a phase that follows Meiosis One and is similar to mitosis, but it starts with cells that already have a haploid number of chromosomes. It further divides these cells into four haploid cells, which are genetically distinct from each other.

Why is it significant that the cells resulting from meiosis are genetically different from each other?

The genetic diversity created by meiosis is significant because it ensures that offspring resulting from sexual reproduction have a unique combination of genetic traits, increasing the adaptability and survival potential of the species.

What type of cells are produced at the end of meiosis, and what is their role?

Meiosis produces gametes, which are sex cells like sperm in males or egg cells in females. These cells are used in fertilization and are essential for sexual reproduction to create a new organism.

How does the process of meiosis relate to the concept of the 'circle of life'?

Meiosis is part of the 'circle of life' as it produces gametes that, when fused with gametes from another organism, can form a fertilized egg. This egg can then undergo mitosis, leading to the development of a new organism and continuing the cycle of life.

In what types of cells does meiosis occur, and where in the body does this typically happen?

Meiosis occurs in germ cells, which are found in the testes in males and the ovaries in females. These cells can undergo meiosis to produce gametes for sexual reproduction.

Why is it important to distinguish between somatic cells and germ cells in the context of mitosis and meiosis?

Somatic cells, which make up most of the body, undergo mitosis for growth and repair, while germ cells undergo meiosis to produce gametes. This distinction is important because it highlights the different roles and processes of cell division in the body.

Outlines

00:00

🌱 Mitosis and Meiosis Overview

This paragraph provides a high-level comparison between mitosis and meiosis. It begins by explaining mitosis, a process where a cell with a diploid number of chromosomes (2n) divides into two identical cells, each with the same genetic information. For humans, this means starting with 46 chromosomes and ending with two cells, each having 46 chromosomes. The process is cyclical, allowing the cells to go through interphase and replicate their DNA, leading to continuous cell growth and division. The paragraph then introduces meiosis, which also starts with a diploid cell but results in two cells with a haploid number of chromosomes (n), halving the genetic information. This process occurs in two phases, Meiosis One and Meiosis Two, and is crucial for the production of gametes (sperm or egg cells) in sexual reproduction. Unlike mitosis, meiosis is not a cycle and leads to the formation of cells that can be used in fertilization.

05:02

🌟 Germ Cells and Their Role in Mitosis and Meiosis

This paragraph delves into the specific types of cells where mitosis and meiosis occur, focusing on germ cells. Germ cells, which are responsible for sexual reproduction, can undergo mitosis to produce more germ cells with a diploid number of chromosomes. Alternatively, they can undergo meiosis to create gametes, which are essential for fertilization. The location of these processes is also highlighted, with male germ cells undergoing these processes in the testes and female germ cells in the ovaries. The distinction between somatic cells, which make up most of the body and undergo mitosis, and germ cells, which are involved in sexual reproduction, is emphasized.

Keywords

💡Mitosis

Mitosis is a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typically diploid. In the video's context, mitosis is essential for growth and repair within an organism, as it allows for the production of somatic cells with identical genetic information. The script explains that after mitosis, the cell can enter the cell cycle again, emphasizing its role in continuous cell division.

💡Diploid

Diploid refers to the state of having two complete sets of chromosomes in a cell, one from each parent. In the script, it is mentioned that a human cell with a diploid number of chromosomes contains 46 chromosomes, arranged in 23 homologous pairs. This term is central to understanding the starting point for both mitosis and meiosis processes described in the video.

💡Chromosomes

Chromosomes are thread-like structures composed of DNA and proteins that carry genetic information. In the video, chromosomes are the units that are replicated and distributed during cell division. The script uses the term to illustrate the difference between the diploid state before cell division and the haploid state after meiosis.

💡Cytokinesis

Cytokinesis is the process by which the cytoplasm of a eukaryotic cell divides after the cell has undergone nuclear division during mitosis. The script briefly mentions cytokinesis as part of the mitosis process, indicating the final step where the cell physically splits into two separate cells.

💡Meiosis

Meiosis is a type of cell division that reduces the chromosome number by half, resulting in the formation of gametes with a haploid set of chromosomes. The video script contrasts meiosis with mitosis, highlighting its role in sexual reproduction and the production of genetically diverse offspring.

💡Haploid

Haploid refers to cells, specifically gametes, that contain half the number of chromosomes of the parent cell, typically one set. The script explains that after meiosis I, the resulting cells are haploid, containing 23 chromosomes, which is crucial for sexual reproduction as it allows for the combination of genetic material from two parents.

💡Homologous Pairs

Homologous pairs are pairs of chromosomes that have the same structure and gene sequence, one inherited from each parent. The script uses this term to describe the initial state of chromosomes before meiosis, where they are divided into individual chromosomes during meiosis I, contributing to genetic diversity.

💡Meiosis One

Meiosis One, also known as the first meiotic division, is the first phase of meiosis where homologous chromosomes are separated into different cells. The script describes this process as the transition from a diploid to a haploid state, emphasizing its importance in the formation of gametes.

💡Meiosis Two

Meiosis Two, or the second meiotic division, is the phase following meiosis I, where the now haploid cells undergo a process similar to mitosis, resulting in four haploid gametes. The script explains that this phase is crucial for the final production of genetically unique sex cells.

💡Gametes

Gametes are the reproductive cells (sperm and egg cells) that fuse during fertilization to form a zygote. The script discusses gametes as the end product of meiosis, which carry half the genetic material necessary for the formation of a new organism.

💡Germ Cells

Germ cells are cells that give rise to gametes and are involved in sexual reproduction. The script mentions that meiosis occurs in germ cells, which are found in the testes for males and ovaries for females, highlighting their role in the production of sex cells.

💡Somatic Cells

Somatic cells are all the body cells except the germ cells. The script contrasts somatic cells with germ cells, indicating that while somatic cells undergo mitosis for growth and repair, germ cells undergo meiosis to produce gametes for reproduction.

Highlights

Mitosis starts with a cell containing a diploid number of chromosomes, denoted as 2n.

Humans have 46 chromosomes, with 23 inherited from each parent, forming 23 homologous pairs.

After mitosis, two cells are produced, each with the same genetic information as the original cell.

Mitosis is a cycle that allows cells to replicate and grow, contributing to the development from a single cell to a complex organism.

Meiosis involves two distinct phases and begins with a cell also containing a diploid number of chromosomes.

Meiosis I results in two cells, each with a haploid number of chromosomes (n), halving the genetic material.

In humans, Meiosis I reduces the chromosome number from 46 to 23 in each resulting cell.

Meiosis II is similar to mitosis but starts with cells that already have a haploid number of chromosomes.

The outcome of Meiosis II is four cells, each with a unique set of haploid chromosomes.

Meiosis involves the random splitting of homologous pairs, contributing to genetic diversity.

Meiosis is not a cycle; the resulting cells are gametes used for sexual reproduction.

In males, meiosis occurs in the testes to produce sperm cells; in females, it occurs in the ovaries to produce egg cells.

Meiosis produces gametes that can fuse during fertilization to form a zygote capable of undergoing mitosis.

The zygote represents the beginning of a new organism, continuing the cycle of life through mitosis.

Somatic cells, which make up most of the body, undergo mitosis, while germ cells can undergo either mitosis or meiosis.

Germ cells can produce other germ cells with a diploid number of chromosomes or gametes with a haploid number.

The location of meiosis within the body is specific to germ cells, either in the testes or ovaries.

Transcripts

- [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.