Cell division - Types and Phases

Cell division is the process in which a cell duplicates itself by dividing its genetic material. For prokaryotes, this process follows simple binary fission in reproduction. In a eukaryotic cell, division for sexual reproduction or vegetative growth occurs through a process involving the replication of DNA, followed by two rounds of division without an intervening round of DNA replication. Students can understand different types of cell division at the organelle level by learning about the appearance of each organelle during interphase and prophase. Our experts at Vedantu have covered everything about cell division for Class 11 students, be it different types of mitosis, meiosis, or any other forms of cell division that you would need to know about.


What is Cell Division?

Cell division can be defined as a process by which a cell distributes its genetic material and cytoplasm and gives rise to new daughter cells. It is a part of the larger cell cycle and has a direct role in cell reproduction.


In well-developed organisms, there are two types of cell division observed, mitosis and meiosis. These are very complex processes that are carried out through different phases. However, if simplified, mitosis can be defined as the exact duplication of a cell where the daughter cells will have the same genetic information as the parent cell. In meiosis, the daughter cells will only have half of the genetic information of the original cell. The common end phase in both processes is cytokinesis and the division of the cytoplasm. We will discuss both types of cell division in this topic.


Cell Division- Mitosis and Meiosis

The two well-documented types of cell division are:

1.Mitosis

2. Meiosis

3. Binary Fission


Mitosis

It is the type of cell division where one cell divides to produce two genetically identical daughter cells. A great majority of cell divisions that take place in our body is mitosis. The process is integral to an organism's body growth and development, and it takes place throughout the organism's lifetime. For some single-celled organisms such as yeast, mitotic cell division is the only way they can reproduce. In the following, we will learn about the mitotic process of cell division.


The cell division phases of mitosis are:

  1. Early and late prophase

  2. Metaphase

  3. Anaphase

  4. Telophase


Before mitosis begins, the cell is in a state called interphase and it copies its DNA and so the chromosomes in the nucleus consist of two copies which are called sister chromatids. In animals, the centrosome is also copied. Centrosomes control mitosis in animal cells. It should be mentioned here, that plant cells do not have centrioles and centrosomes, and the microtubule-organizing center regulates mitosis.


Early and Late Prophase

  • In the early prophase, the cell initiates cell division by breaking down some cell components and building other components and then the chromosome division starts.

  • In this stage, the chromosomes start to condense which helps them to separate easily in later stages

  • Afterwards, the mitotic spindle starts to form, a structure made of microtubules. It organizes the chromosomes and moves them around during mitosis. The mitotic spindle grows between the centrosomes of the cell as they move towards different poles.

  • The nucleolus then disappears which is a sign that the nucleus is getting ready to break down.

  • In the late prophase which is also called prometaphase, the mitotic spindle starts to organize the chromosomes.

  • Once the chromosomes finish condensing, they form a compact structure.

  • Then the nuclear envelope breaks down and the chromosomes are released.

  • At the end of the prophase, the mitotic spindle grows, and some microtubules start to capture and organize chromosomes.


Metaphase

  • Metaphase starts when the mitotic spindle organizes all chromosomes and lines them up in the middle of the cell to divide.

  • All chromosomes align at the metaphase plate.

  • At this stage of metaphase, the two kinetochores of each chromosome should be attached to microtubules from opposite spindle poles. Before proceeding forward to anaphase, the cell will check if all kinetochores are properly attached to microtubules and it is called spindle checkpoint.

  • The spindle checkpoint ensures that the sister chromatids are split equally into two daughter cells.


Anaphase

  • In this stage, the sister chromatids separate from each other and move towards the opposite poles of the cell. The protein glue that holds them breaks and allows them to separate.

  • Microtubules that are not attached to chromosomes elongate and push apart. In doing so they separate the poles and makes the cell longer. These processes are controlled by motor proteins and these proteins carry the chromosomes and microtubules as they move.


Telophase

  • In this stage, the cell is almost divided and starts to re-establish its normal cellular structures as cytokinesis takes place.

  • The mitotic spindle breaks down into its building blocks and two new nuclei are formed, one for each set of chromosomes. 

  • The nuclear membrane and the nucleoli then reappear and the chromosomes begin to de- condense to return to their normal form.


Cytokinesis

  • In animal cells, cytokinesis is contractile. There's a pinch-like formation within the cell which divides it in two like a coin purse with a 'drawstring'. The "drawstring" is a band of actin protein filaments. The pinch crease is called the cleavage furrow.

  • Plant cells can't be divided like this as they have a rigid cell wall and are too stiff. A cell plate forms down the middle of the cell which splits the daughter cells. 


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Meiosis

In meiosis, a single cell divides twice to produce four cells that contain half of the original amount of genetic material. It can be observed in sperm cells in males and egg cells in females. 


There are 9 meiotic cell division phases. These are discussed below:

Interphase

  • Similar to mitosis the genetic material of the cell is copied and two identical sets of chromosomes are formed.

  • The centrosomes and the centrioles are also copied and in this phase, the microtubules extend from centrosomes.


Prophase I

  • The two sets of chromosomes condense into an X-shaped formation 

  • Each chromosome consists of two sister chromatids which contain identical genetic information.

  • All chromosomes pair up. For example, both copies of chromosome 1 and both copies of chromosome 2 are together.

  • The chromosome pairs may then exchange parts of DNA through crossing over or recombination.

  • In the end, in this stage, the nuclear membrane dissolves and releases the chromosomes.

  • The meiotic spindle which consists of microtubules and other proteins extends across the cell.


Metaphase I

  • The chromosome pairs align next to each other along the center of the cell.

  • The centrioles move at the opposite poles of the cell and the meiotic spindles extend from them. Their fibers attach to one chromosome of each pair. 


Anaphase I

  • The chromosome pairs are then separated by the meiotic spindle and move one chromosome to opposite poles of the cell.

  • In meiosis, the sister chromatids of the cell stay together.


Telophase I and Cytokinesis

  • The chromosomes move to opposite poles of a cell and each pole has a full set of chromosomes.

  • A nuclear membrane starts to form around each set of chromosomes to form two new nuclei.

  • Cytokinesis takes place and two daughter cells are produced.


Meiosis II

Prophase II

  • At the end of meiosis, there are two daughter cells with 23 chromosomes

  • The chromosomes condense again and form visible X-shaped structures 

  • The nuclear membrane will dissolve releasing the chromosomes.

  • The centrioles duplicate and the meiotic spindle is formed.


Metaphase II

  • Similar to metaphase I, the sister chromatid align along the center of the cell

  • The centrioles move to opposite poles of the daughter cells.

  • Meiotic spindle fibers attach to individual sister chromatids.


Anaphase II

  • The sister chromatids are separated and moved to opposite poles by the meiotic spindle and they become individual chromosomes.


Telophase II and Cytokinesis

  • The chromosomes move to opposite poles of the cell and each pole has a full set of chromosomes.

  • A nuclear membrane starts to form again and two new cell nuclei are formed.

  • Cytokinesis takes place.

  • Once cytokinesis is completed there are four new cells, with a haploid set of chromosomes

  • In males, all four cells are sperm cells

  • In females, one new is an egg cell and the others are polar bodies


Binary Fission

When a cell divides, it first duplicates its DNA, then divides. This is how the day-to-day growth of the human body occurs, which requires new cells to be created for tissue repair and maintenance through cell division. For prokaryotes (bacteria), the process of binary fission is a simple duplication of the DNA followed by division into two cells. For eukaryotes (plants and animals), the process of cell division is more complicated. The first step in cell division for most cells is the duplication of the chromosomes. A single set of chromosomes in a normal human cell contains approximately three billion base pairs or six billion nucleotides.


Conclusion

Cell Division can be simply defined as the process that results in two daughter cells, each with the same number of chromosomes as the parent cell. The chromosomes are duplicated first, and then the cell divides. In prokaryotes, binary fission is a simple duplication of the DNA followed by division into two cells. For eukaryotes, the process of cell division is more complicated. The first step in cell division for most cells is the duplication of the chromosomes. A single set of chromosomes in a normal human cell contains approximately three billion base pairs or six billion nucleotides.


In meiosis, I, the sister chromatids of the cell stay together. When the cells divide, it forms four new cells, with a haploid set of chromosomes. In males, all four cells are sperm cells. One new is an egg cell in females, and the others are polar bodies. So, meiosis is important in the process of sexual reproduction. One should know that meiosis II is complete and the cells divide into four new daughter cells.

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FAQs on Cell division

1. What is the cell division cycle?

The cell division cycle or the cycle is a series of events that takes place in a cell which causes the cell into two daughter cells. It consists of two primary phases

  1. Interphase

  2. M phase

Interphase: It is an active phase between subsequent cell divisions. This consists of multiple phases. These are

  • G0: It is the resting phase between cell divisions

  • G1: The cell shows metabolic activity and grows continuously

  • S phase: DNA duplication takes place in this phase

  • G2: Protein synthesis takes place

  • Quiescent stage: The cell does not undergo further division and exits the G1 stage and enter the inactive stage.

M phase: Cell division takes place in this phase. It consists of 2 phases:

  1. Karyokinesis

  2. Cytokinesis

2. Why is cell division necessary?

Cell division serves as a means of cell reproduction in both unicellular and multicellular organisms. In unicellular organisms, reproduction takes place through binary fission which is a type of mitotic division. In multicellular organisms, cell division assists in the formation of gametes which combine to produce organisms. Cell division also plays a role in the growth and development of an organism and repairs injuries.

3. What is mitosis?

Mitosis is the process of cell division in which a single cell divides to form two genetically identical daughter cells. It occurs in somatic cells (cells other than gametes). One should note that mitosis and meiosis are different processes. Meiosis is the process of cell division in which a single cell divides to form four genetically different daughter cells. It occurs in gametes (sperm and egg cells). Somatic cells and germ cells follow different processes of cell division. The phases of mitosis and meiosis are the same, but the resulting cells are different. Students should be careful not to confuse the two processes. Vedantu provides the best online tutoring for students who want to score well in their studies. With our online tutoring, we assure success to all students.

4. What is an allele, and why does it matter for meiosis?

An allele is one of two or more versions of a gene. Alleles determine physical traits, such as eye color and blood type. When the alleles for these genes are different, individuals can pass them on to their offspring. The combination of alleles in an individual's parents determines which form of the gene that individual inherits. This is why two individuals with blue eyes can have a brown-eyed child.


An allele is one of the variants of a gene that are located at the same place on a chromosome and that determine, together with other genes in the same genome, some typical traits. These typical traits are called "phenotypes". For example, there could be different alleles for eye color or blood type. The different versions are called "genotypes".

5. How does mitosis occur?

Mitosis is the process of cell division in which a single cell divides into two identical daughter cells. The different phases in mitosis are prophase, prometaphase, metaphase, anaphase, and telophase.


Mitosis is a type of cell division in which a single eukaryotic cell divides into two genetically identical daughter cells. The process of mitosis is divided into five phases: prophase, prometaphase, metaphase, anaphase, and telophase. During these phases, the cell goes through a series of changes that result in two daughter cells that are genetically identical to one another. Mitosis is used by the body to create new cells for growth and repair.

6. What are sister chromatids?

Sister chromatids are two identical copies of a chromosome that are attached to one another. They form during replication when the DNA is copied. Each sister chromatid has the same genetic information as the other.


Sister chromatids are two chromosomes that are attached and that have the same genetic information. They form during replication when the DNA is copied. This means that each sister chromatid has the same genes as the other. Sister chromatids stay together during cell division and move to opposite poles of the cell. This ensures that the daughter cells receive an identical set of chromosomes.

7. What are chromosomes?

Chromosomes are structures in the cell nucleus that carry the genes. The human body has 46 chromosomes, 23 from each parent. Chromosomes are made up of DNA and proteins.


Chromosomes are structures in the cell nucleus that carry the genes. The human body has 46 chromosomes, 23 from each parent. Chromosomes are made up of DNA and proteins. Students should be careful not to confuse chromosomes with genes. Chromosomes are structures that carry genes. Genes are the units of DNA that make up the chromosomes.


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