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When does meiosis exactly occur?I mean to say like mitosis occurs during the m phase of cell cycle in which part does meiosis occur?
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The cell cycle

Living cells go through a series of stages known as the cell cycle. The cells grow, copy their chromosomes, and then divide to form new cells.The Cell Cycle -Cell Cycle And Cell Division,Class 11, Biology - NEET

The cell cycle


G1 phase. The cell grows.

S phase. The cell makes copies of its chromosomes. Each chromosome now consists of two sister chromatids.

G2 phase. The cell checks the duplicated chromosomes and gets ready to divide.

M phase. The cell separates the copied chromosomes to form two full sets (mitosis) and the cell divides into two new cells (cytokinesis).

The period between cell divisions is known as 'interphase'.

Cells that are not dividing leave the cell cycle and stay in G0.

Mitosis and meiosis

Cells divide into two different ways to make new cells.

Mitosis

Mitosis is used to produce daughter cells that are genetically identical to the parent cells. The cell copies - or 'replicates' - its chromosomes, and then splits the copied chromosomes equally to make sure that each daughter cell has a full set.

Meiosis

Meiosis is used to make special cells - sperm cells and egg cells - that have half the normal number of chromosomes. It reduces the number from 23 pairs of chromosomes to 23 single chromosomes. The cell copies its chromosomes, but then separates the 23 pairs to ensure that each daughter cell has only one copy of each chromosome. A second division that divides each daughter cell again to produce four daughter cells.
The Cell Cycle -Cell Cycle And Cell Division,Class 11, Biology - NEET 

 

Mitosis and meiosis

Mitosis

Your body contains trillions of cells (thousands of millions). But you started life as a single cell - a fertilised egg cell. This cell then divided and divided to make more cells through a process called mitosis.

Mitosis is a way of making more cells that are genetically the same as the parent cell. It plays an important part in the development of embryos, and it is important for the growth and development of our bodies as well. Mitosis produces new cells, and replaces cells that are old, lost or damaged.

In mitosis a cell divides to form two identical daughter cells. It is important that the daughter cells have a copy of every chromosome, so the process involves copying the chromosomes first and then carefully separating the copies to give each new cell a full set.

Before mitosis, the chromosomes are copied. They then coil up, and each chromosome looks like a letter X in the nucleus of the cell. The chromosomes now consist of two sister chromatids. Mitosis separates these chromatids, so that each new cell has a copy of every chromosome.
The Cell Cycle -Cell Cycle And Cell Division,Class 11, Biology - NEET 

 

A diagram of a cell ready for mitosis. The copied chromosomes consist of two chromatids joined at the centromere


The process of mitosis involves a number of different stages. The following diagram sets out the stages, and the main events that occur in each stage.The Cell Cycle -Cell Cycle And Cell Division,Class 11, Biology - NEET

 

The phases of mitosis

 

Meiosis

Some simple organisms - such as bacteria - can reproduce by simply dividing into two new individuals. Other organisms, including human beings, reproduce through sexual reproduction. New individuals are formed by the joining together of two special cells: a sperm cell and an egg cell.

The cells in our bodies contain 23 pairs of chromosomes - giving us 46 chromosomes in total. Sperm cells and egg cells contain 23 single chromosomes, half the normal number, and are made by a special form of cell division called meiosis.

Meiosis separates the pairs of matching (or 'homologous') chromosomes, so that sperm cells and egg cells have only one copy of each. That way, when an egg cell fuses with a sperm cell, the fertilised egg has a full set: that is, two copies of every chromosome.

Meiosis involves two cell divisions: Meiosis I and Meiosis II.

Meiosis I separates the matching - or 'homologous' - pairs of chromosomes.
Meiosis II divides each chromosome into two copies (much like mitosis).
In Meiosis I, each daughter cell receives a mix of chromosomes from the two sets in the parent cell. In addition, the chromosomes in each matching pair swap some genetic material before they are parted in a process called crossing over. These processes produce new combinations of genes in the sperm cells and egg cells.

The following diagrams set out the main stages of Meiosis I and Meiosis II in males. (A similar process in females produces egg cells rather than sperm cells.)The Cell Cycle -Cell Cycle And Cell Division,Class 11, Biology - NEET

The Cell Cycle -Cell Cycle And Cell Division,Class 11, Biology - NEET 

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FAQs on The Cell Cycle -Cell Cycle And Cell Division,Class 11, Biology - NEET

1. What is the cell cycle and why is it important?
Ans. The cell cycle refers to the series of events that occur in a cell, leading to its growth, replication, and division into two daughter cells. It is important as it ensures the proper growth and development of organisms, tissue repair, and maintenance of cell populations in multicellular organisms.
2. What are the different phases of the cell cycle?
Ans. The cell cycle consists of four main phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). During G1 phase, the cell grows and performs its normal functions. In the S phase, DNA replication occurs. G2 phase is the preparation phase for cell division, and during the M phase, the cell undergoes mitosis or meiosis to form two daughter cells.
3. What is the role of checkpoints in the cell cycle?
Ans. Checkpoints are regulatory mechanisms in the cell cycle that ensure the proper progression and integrity of the cell cycle. They monitor DNA integrity, cell size, and proper replication before allowing the cell to proceed to the next phase. Checkpoints help prevent the formation of abnormal cells and maintain genomic stability.
4. How is cell division regulated in the cell cycle?
Ans. Cell division is regulated by a complex interplay of various proteins and signaling pathways. Cyclins and cyclin-dependent kinases (CDKs) play a crucial role in regulating the cell cycle. Cyclins bind to CDKs to activate them, which in turn phosphorylate target proteins to initiate specific cell cycle events. The activity of CDKs is tightly regulated by the presence or absence of specific cyclins.
5. What are the consequences of abnormal cell cycle regulation?
Ans. Abnormal cell cycle regulation can lead to various consequences, including uncontrolled cell growth and division, which can result in the formation of tumors and cancer. It can also lead to cellular senescence or programmed cell death. Dysregulation of the cell cycle can disrupt normal development and cellular functions, leading to various diseases and disorders.
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