Mitosis & Meiosis - Online Tutor, Practice Problems & Exam Prep

Mitosis is the asexual division of a diploid somatic cell, resulting in two genetically identical diploid cells. It consists of five phases: prophase, prometaphase, metaphase, anaphase, and telophase, followed by cytokinesis. Meiosis, starting with a diploid germ cell, produces four genetically diverse haploid gametes through two rounds of division: meiosis I (reductional) and meiosis II (equational). Understanding these processes is crucial for grasping cellular reproduction and genetic diversity.

Mitosis

In this video, we're going to begin our lesson on mitosis and meiosis. Rather than dividing by binary fission, like what prokaryotic cells do, eukaryotic cells will divide via the process of either mitosis or meiosis. In this video, we're going to do a quick overview of mitosis, but later in our course in a different video, we'll do a quick overview of meiosis. Keep in mind that for this process of mitosis, we have other videos in our biology course that go into a lot more detail. If you need those videos from your old biology courses be sure to go back and check out those videos in our biology course.

So that being said, mitosis is defined as the asexual process of dividing the nucleus and the genetic material within the nucleus. Mitosis can be defined as division of the nucleus. Mitosis will occur in a specific set of cells known as somatic cells, which are really just body cells and include all types of cells except for the gametes or the sex cells. Mitosis is going to start with just one diploid cell or one cell that has two copies of every chromosome. But mitosis ends with two genetically identical cells, meaning they have exactly the same DNA, and those cells will be diploid as well. Meaning once again that they have two copies of every chromosome.

As you can see by this image down below, mitosis actually consists of five different phases which are prophase, prometaphase, metaphase, anaphase, and telophase. In each of these phases, there are characteristic events that occur that we cover all of those characteristic events in our biology videos and our biology course. However, just to do a brief recap of these events: in prophase, what happens is the chromatin is going to coil down and condense into tightly coiled chromosomes that are distinct and visible under a microscope. Then the mitotic spindle is also going to begin to form, which is made of microtubules.

In prometaphase, the mitotic spindle is going to attach to each of the chromosomes at these proteins called kinetochores, which in this image are these little green circles that you see, right in the middle here. Then, the nuclear envelope is also going to break down. In metaphase, all of the chromosomes are going to line up in a single file row right in the middle of the cell. In anaphase, the sister chromatids are going to be pulled apart from one another, so that each pole gets an identical copy of the DNA.

Telophase is the last phase, which is pretty much the reverse of prophase and prometaphase. The nuclear envelope is going to form, the mitotic spindle breaks down, the tightly coiled chromosomes uncoil and unravel back into chromatin. Following telophase is the process of cytokinesis, which will actually split the cell cytoplasm and split the cell into two. This is the overview of mitosis here, and in our next lesson video, we'll be able to talk about a little memory tool for how you can go about memorizing the order of the phases of mitosis. And then later we'll get to talk more about meiosis. I'll see you all in our next video.

How to Remember the Order of the Phases of Mitosis

In this video, we're going to talk about how to remember the order of the phases of mitosis. This is a strategy that is really effective for me, and if it's effective for me, I believe that it can also be effective for you as well. When you're thinking about the order of the phases of mitosis, personally, I think about the M in Metaphase, and that's because I think that the M in Metaphase is the M in the word middle. I know that metaphase is going to be the phase that's right in the middle. If I know that there are 5 phases total, metaphase is going to be the one in the middle, and that means that there are going to be 2 phases that come before and there are going to be 2 phases that come after. I start here with metaphase being the middle phase.

Then, what you need to know is that the root "pro" is a root that means before. Prometaphase and prophase both have this root that means before. Prometaphase is going to be the phase that comes just before metaphase. Prophase is just going to come before everything else and so prophase – the root pro again means before – so it just comes before everything. Now you've got these first three in the correct order.

Then, you think about the A in anaphase, and I think, hey, the A in anaphase is for the A in after. Anaphase is going to come just after the middle phase, metaphase, so it comes right here at this position. Then you think about the T in telophase, and you think, hey. The T in telophase is for the T in tail end, because telophase is coming at the tail end of mitosis. If you're able to remember these details, then you'll be able to remember the order of the phases of mitosis no problem every time.

This here concludes our lesson on how to remember the order of the phases of mitosis, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.

The correct sequence for the phases of mitosis is:

• A. a) Prophase - prometaphase - anaphase - metaphase – telophase.
• B. b) Prophase - prometaphase - metaphase - anaphase – telophase.
• C. c) Prometaphase - prophase - metaphase - anaphase – telophase.
• D. d) Metaphase - anaphase - interphase - prophase – telophase

Meiosis

In this video, we're going to begin our overview of meiosis, which is one of the ways that some specialized eukaryotic cells can divide. Now, one thing I want to point out before we continue is that in this video we're only going to be doing an overview of meiosis. And in our biology course, we have a set of videos that go into a lot more details of both mitosis and meiosis. And so if you need to, make sure to go check those out. Meiosis is actually going to start with a diploid cell, just like mitosis starts with a diploid cell. However, in meiosis, the diploid cell is a specialized cell called a germ cell. A germ cell is the precursor cell to what are known as gametes or sex cells, such as sperm in males and eggs in females. Meiosis is going to start with a diploid germ cell, but meiosis is actually going to end with 4 genetically diverse cells or 4 cells that have different or unique DNA. And these cells are going to be haploid gametes, meaning that they have only one copy of every chromosome or half the number of chromosomes as a diploid cell. And once again, they are gametes, which means that they are sex cells such as, again, sperm in males or eggs in females. Now the overall process of meiosis is actually broken down into two rounds of cell division that scientists refer to as meiosis 1 and meiosis 2. Now meiosis 1 is also sometimes referred to as reductional division because it reduces the ploidy number. And the ploidy is just referring to the number of sets of chromosomes. And it does this by separating homologous chromosomes. And so in meiosis 1, basically what happens is a diploid germ cell, and diploid is also represented by the variable 2n, a diploid germ cell is going to divide into two haploid daughter cells. And so, this is just the first round of cell division in meiosis, so this is the halfway point of meiosis. And so in the second round of cell division in meiosis, in meiosis 2, which is known as equational division because it maintains an equal ploidy number after the division, meaning that it maintains the same number of sets of chromosomes. And so it does this by separating what are known as sister chromatids rather than separating homologous chromosomes. And so, essentially what happens in meiosis 2, which is a continuation of meiosis 1, the haploid cells from meiosis 1 are going to each divide, producing a total of 4, once again, genetically diverse haploid gametes as we mentioned up above here. And so if we take a look at this image down below, we can get a better understanding of this overview of meiosis, which again is broken up into meiosis 1 and meiosis 2. And so notice over here on the left-hand side, we're showing you a germ cell, which is a diploid cell, and that's represented by 2n. And so in interphase 1, which is the phase that occurs before meiosis even begins, the germ cell is going to replicate its DNA. It's going to duplicate its DNA. And then it will enter into meiosis 1 or reductional division which is represented here in this phase. And so in this meiosis 1 cell division, basically this germ cell is going to divide to produce two haploid daughter cells. And, it's gone from being a diploid cell to haploid cells, which means that it is a division because the ploidy numbers decreased. And then, what we have here is meiosis 2 follows meiosis 1, it's really a continuation. And so each of these haploid cells is going to divide to create a total of 4 cells as you see here. And these 4 cells are going to be haploid gametes. Once again meaning that they have half the number of chromosomes and that they would turn into either a sperm cell in males or an egg cell in females. And so really this process of meiosis is used specifically for forming gametes, the formation of sex cells. And so this here concludes our brief overview of meiosis, and once again, if you need more details of meiosis, be sure to go check out those videos that we have in our biology course. That being said, I'll see you all in our next video.

In Meiosis I, cytokinesis usually occurs after telophase I and produces:

a) Four diploid cells.

b) Two haploid cells.

c) Four haploid cells.

d) Two diploid cells.

• A. Four diploid cells.
• B. Two haploid cells.
• C. Four haploid cells.
• D. Two diploid cells.

In Meiosis II, ________ cells are divided into 4 ___________ daughter cells.

a) Diploid; Haploid.

b) Haploid; Diploid.

c) Haploid; Haploid.

d) Diploid; Diploid.

• A. Diploid; Haploid.
• B. Haploid; Diploid.
• C. Haploid; Haploid.
• D. Diploid; Diploid.

Here’s what students ask on this topic:

What are the main differences between mitosis and meiosis?

Mitosis and meiosis are both processes of cell division, but they serve different purposes and have distinct outcomes. Mitosis occurs in somatic cells and results in two genetically identical diploid cells, each with two copies of every chromosome. It consists of five phases: prophase, prometaphase, metaphase, anaphase, and telophase, followed by cytokinesis. Meiosis, on the other hand, occurs in germ cells and produces four genetically diverse haploid gametes, each with one copy of every chromosome. Meiosis involves two rounds of division: meiosis I (reductional division) and meiosis II (equational division). The key differences lie in the number of divisions, the type of cells produced, and the genetic diversity of the resulting cells.

What are the phases of mitosis and their key events?

Mitosis consists of five phases: prophase, prometaphase, metaphase, anaphase, and telophase. In prophase, chromatin condenses into visible chromosomes, and the mitotic spindle begins to form. During prometaphase, the nuclear envelope breaks down, and spindle fibers attach to chromosomes at kinetochores. In metaphase, chromosomes align in the middle of the cell. Anaphase follows, where sister chromatids are pulled apart to opposite poles. Finally, in telophase, the nuclear envelope re-forms around each set of chromosomes, and the chromosomes decondense back into chromatin. Cytokinesis, the division of the cytoplasm, usually follows telophase, resulting in two identical daughter cells.

How does meiosis contribute to genetic diversity?

Meiosis contributes to genetic diversity through two main mechanisms: crossing over and independent assortment. During prophase I of meiosis I, homologous chromosomes pair up and exchange genetic material in a process called crossing over. This results in new combinations of alleles on each chromosome. Additionally, during metaphase I, homologous chromosome pairs align randomly at the cell's equator, leading to independent assortment. This random alignment means that the combination of chromosomes that end up in each gamete is unique. These processes ensure that each of the four haploid gametes produced by meiosis has a different genetic makeup, contributing to genetic diversity in sexually reproducing populations.

What is the significance of the reductional and equational divisions in meiosis?

Meiosis consists of two rounds of division: meiosis I (reductional division) and meiosis II (equational division). The reductional division in meiosis I is significant because it reduces the chromosome number by half, from diploid (2n) to haploid (n). This is achieved by separating homologous chromosomes, ensuring that each daughter cell receives only one chromosome from each pair. Meiosis II, the equational division, is similar to mitosis and separates sister chromatids, maintaining the haploid number of chromosomes. Together, these divisions ensure that gametes have half the chromosome number of the original germ cell, which is crucial for maintaining the species' chromosome number during sexual reproduction.

What is the role of cytokinesis in cell division?

Cytokinesis is the process that follows the completion of mitosis or meiosis, involving the division of the cell's cytoplasm to form two separate daughter cells. In mitosis, cytokinesis ensures that each of the two genetically identical daughter cells receives an equal share of the cytoplasm and organelles. In meiosis, cytokinesis occurs twice, once after meiosis I and again after meiosis II, resulting in four haploid gametes. The role of cytokinesis is crucial for the physical separation of the daughter cells, allowing them to function independently and ensuring proper cell function and development.