The 2nd division in meiosis is similar to mitosis division without first copying the dna.

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.

• 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.

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 copied chromosomes consist of two chromatids joined at the centromere.

The process of mitosis involves a number of different stages.

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.

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.

Cells divide and reproduce in two ways: mitosis and meiosis. Mitosis is a process of cell division that results in two genetically identical daughter cells developing from a single parent cell. Mitosis is used by single-celled organisms to reproduce; it is also used for the organic growth of tissues, fibers, and membranes.

Meiosis, on the other hand, is the division of a germ cell involving two fissions of the nucleus and giving rise to four gametes, or sex cells, each possessing half the number of chromosomes of the original cell. Meiosis plays a role in sexual reproduction of organisms. The male and female sex cells (i.e., egg and sperm) are the end result of meiosis; they combine to create new, genetically different offspring.

What is the role and purpose of mitosis and meiosis?

Though both types of cell division are found in many animals, plants, and fungi, mitosis is more common than meiosis and has a wider variety of functions. Not only is mitosis responsible for asexual reproduction in single-celled organisms, but it is also what enables cellular growth and repair in multicellular organisms, such as humans. In mitosis, a cell makes an exact clone of itself. This process is what is behind the growth of children into adults, the healing of cuts and bruises, and even the regrowth of skin, limbs, and appendages in animals like geckos and lizards.

Meiosis is a more specific type of cell division (of germ cells, in particular) that results in gametes, either eggs or sperm, that contain half of the chromosomes found in a parent cell. Unlike mitosis with its many functions, meiosis has a narrow but significant purpose: assisting sexual reproduction. It is the process that enables children to be related but still different from their two parents.

Meiosis and Genetic Diversity

Sexual reproduction uses the process of meiosis to increase genetic diversity. Offspring created through asexual reproduction (mitosis) are genetically identical to their parent, but the germ cells created during meiosis are different from their parent cells. Some mutations frequently occur during meiosis. Further, germ cells have only one set of chromosomes, so two germ cells are required to make a complete set of genetic material for the offspring. The offspring is therefore able to inherit genes from both parents and both sets of grandparents.

Genetic diversity makes a population more resilient and adaptable to the environment, which increases chances of survival and evolution for the long term.

Mitosis as a form of reproduction for single-cell organisms originated with life itself, around 3.8 billion years ago. Meiosis is thought to have appeared around 1.4 billion years ago.

Mitosis and Meiosis Stages

Cells spend about 90% of their existence in a stage known as interphase. Because cells function more efficiently and reliably when small, most cells carry out regular metabolic tasks, divide, or die, rather than simply grow larger in the interphase. Cells "prepare" for division by replicating DNA and duplicating protein-based centrioles. When cell division begins, the cells enter into either mitotic or meiotic phases.

In mitosis, the end product is two cells: the original parent cell and a new, genetically identical daughter cell. Meiosis is more complex and goes through additional phases to create four genetically different haploid cells which then have the potential to combine and form a new, genetically diverse diploid offspring.

Stages of Mitosis

What are the four stages of mitosis?

There are four mitotic phases: prophase, metaphase, anaphase, and telophase. Plant cells have an additional phase, preprophase, that occurs before prophase.

• During the mitotic prophase, the nuclear membrane (sometimes called "envelope") dissolves. Interphase's chromatin tightly coils and condenses until it becomes chromosomes. These chromosomes are made up of two genetically identical sister chromatids that are joined together by a centromere. Centrosomes move away from the nucleus in opposite directions, leaving behind a spindle apparatus.

• In metaphase, motor proteins found on either side of the chromosomes' centromeres help move the chromosomes according to the pull of the opposing centrosomes, eventually placing them in a vertical line down the center of the cell; this is sometimes known as the metaphase plate or spindle equator.

• The spindle fibers begin to shorten during anaphase, pulling the sister chromatids apart at their centromeres. These split chromosomes are dragged toward the centrosomes found at opposite ends of the cell, making many of the chromatids briefly appear "V" shaped. The two split portions of the cell are officially known as "daughter chromosomes" at this point in the cell cycle.

• Telophase is the final phase of mitotic cell division. During telophase, the daughter chromosomes attach to their respective ends of the parent cell. Previous phases are repeated, only in reverse. The spindle apparatus dissolves, and nuclear membranes form around the separated daughter chromosomes. Within these newly formed nuclei, the chromosomes uncoil and return to a chromatin state.

• One final process—cytokinesis—is required for the daughter chromosomes to become daughter cells. Cytokinesis is not part of the cell division process, but it marks the end of the cell cycle and is the process by which the daughter chromosomes separate into two new, unique cells. Thanks to mitosis, these two new cells are genetically identical to each other and to their original parent cell; they now enter their own individual interphases.

Stages of Meiosis

There are two primary meiosis stages in which cell division occurs: meiosis 1 and meiosis 2. Both primary stages have four stages of their own. Meiosis 1 has prophase 1, metaphase 1, anaphase 1, and telophase 1, while meiosis 2 has prophase 2, metaphase 2, anaphase 2, and telophase 2. Cytokinesis plays a role in meiosis, too; however, as in mitosis, it is a separate process from meiosis itself, and cytokinesis shows up at a different point in the division.

Meiosis I vs. Meiosis II

See a detailed comparison of Meiosis I and Meiosis II.

In meiosis 1, a germ cell divides into two haploid cells (halving the number of chromosomes in the process), and the main focus is on the exchange of similar genetic material (e.g., a hair gene; see also genotype vs phenotype). In meiosis 2, which is quite similar to mitosis, the two diploid cells further divide into four haploid cells.

Stages of Meiosis I

• The first meiotic phase is prophase 1. As in mitosis, the nuclear membrane dissolves, chromosomes develop from the chromatin, and the centrosomes push apart, creating the spindle apparatus. Homologous (similar) chromosomes from both parents pair up and exchange DNA in a process known as crossing over. This results in genetic diversity. These paired up chromosomes—two from each parent—are called tetrads.

• In metaphase 1, some of the spindle fibers attach to the chromosomes' centromeres. The fibers pull the tetrads into a vertical line along the center of the cell.

• Anaphase 1 is when the tetrads are pulled apart from each other, with half the pairs going to one side of the cell and the other half going to the opposite side. It is important to understand that whole chromosomes are moving in this process, not chromatids, as is the case in mitosis.

• At some point between the end of anaphase 1 and the developments of telophase 1, cytokinesis begins splitting the cell into two daughter cells. In telophase 1, The spindle apparatus dissolves, and nuclear membranes develop around the chromosomes that are now found at opposite sides of the parent cell / new cells.

Stages of Meiosis II

• In prophase 2, centrosomes form and push apart in the two new cells. A spindle apparatus develops, and the cells' nuclear membranes dissolve.

• Spindle fibers connect to chromosome centromeres in metaphase 2 and line the chromosomes up along the cell equator.

• During anaphase 2, the chromosomes' centromeres break, and the spindle fibers pull the chromatids apart. The two split portions of the cells are officially known as "sister chromosomes" at this point.

• As in telophase 1, telophase 2 is aided by cytokinesis, which splits both cells yet again, resulting in four haploid cells called gametes. Nuclear membranes develop in these cells, which again enter their own interphases.

References

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