All cell arise from other cells with the process of cell division. Meiosis is a committed form of cell division that produce reproductive cells, such together plant and fungal spores and also sperm and egg cells.

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In general, this procedure involves a "parent" cell separating into two or much more "daughter" cells. In this way, the parent cell have the right to pass top top its hereditary material from generation come generation.

eukaryotic cells and their chromosomes

Based on the relative complexity of their cells, all living organisms are generally classified as either prokaryotes or eukaryotes. Prokaryotes, such as bacteria, covers a solitary cell v a simple internal structure. Their DNA floats freely within the cell in a twisted, thread-like mass referred to as the nucleoid.


Animals, plants and fungi are all eukaryotes. Eukaryotic cells have dedicated components called organelles, such as mitochondria, chloroplasts and also the endoplasmic reticulum. Every of these performs a certain function. Unlike prokaryotes, eukaryotic bio DNA is packed within a main compartment referred to as the nucleus.


Within the eukaryotic nucleus, long double-helical strands that DNA are wrapped tightly roughly proteins called histones. This forms a rod-like structure referred to as the chromosome.


Cells in the person body have actually 23 pairs of chromosomes, or 46 in total. This includes two sex chromosomes: 2 X chromosomes because that females and one X and also one Y chromosome for males. Due to the fact that each chromosome has a pair, these cells are referred to as "diploid" cells.

On the various other hand, human spermand egg cells have actually only 23 chromosomes, or half the chromosomes that a diploid cell. Thus, castle are referred to as "haploid" cells.

When the sperm and also egg incorporate during fertilization, the total chromosome number is restored. That"s due to the fact that sexually reproducing organisms get a collection of chromosomes from every parent: a maternal and also paternal set.Each chromosome has actually a corresponding pair, orhomolog.

Mitosis vs. Meiosis

Eukaryotesare capable of two types of cabinet division: mitosisand meiosis

Mitosis enables for cells to develop identical copies of themselves, which method the hereditary material is copied from parental to daughter cells. Mitosis produces 2 daughter cells from one parental cell.

Single-celled eukaryotes, such together amoeba and yeast, usage mitosis to reproduce asexuallyand rise their population. Multicell eukaryotes, like humans, use mitosis to thrive or heal hurt tissues.

Meiosis, ~ above the various other hand, is a devoted form the cell department that wake up in organisms that reproduce sexually. As discussed above, it produces reproductive cells, such as sperm cells, egg cells, and spores in plants and fungi.

In humans, one-of-a-kind cells called germ cell undergo meiosis and ultimately give rise to sperm or eggs. Germ cells contain a complete set of 46 chromosomes (23 maternal chromosomes and 23 paternal chromosomes). By the finish of meiosis, the resulting reproductive cells, orgametes, each have actually 23 genetically distinct chromosomes.

The overall procedure of meiosis produces 4 daughter cell from one single parent cell. Each daughter cabinet is haploid, since it has half the variety of chromosomes together the initial parent cell.

"Meiosis is reductional," said M. Andrew Hoyt, a biologist and also professor at Johns Hopkins University.

Unlike in mitosis, the daughter cells produced during meiosis room genetically diverse. Homologous chromosomes exchange bits that DNA to create genetically unique, hybrid chromosomes destined because that each daughter cell.

A closer look at meiosis

Before meiosis begins, part important alters take place within the parent cells. First, every chromosome create a copy that itself. These copied chromosomes are well-known as sisters chromatids. They are fused together and the point where they are joined is recognized as the centromere. Unify sister chromatids around resemble the form of the letter "X."

Meiosis occurs end the course of two rounds of atom divisions, dubbed meiosis I and also meiosis II, according to Nature Education"s Scitable. Furthermore, meiosis I and also II are each separated into four major stages: prophase, metaphase, anaphase and also telophase.

Meiosis ns is responsible for creating genetically distinctive chromosomes. Sister chromatids pair up v their homologs and also exchange genetic material v one another. At the finish of this division, one parent cell produces two daughter cells, each carrying one set of sisters chromatids.

Meiosis II very closely resembles mitosis. The 2 daughter cell move right into this phase without any type of further chromosome duplication. The sister chromatids are pulled apart during this division. A full of 4 haploid daughter cell are produced during the course of meiosis II.


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Meiosis is the procedure whereby chromosomes are copied, paired up and also separated to create eggs or sperm. (Image credit: NIGMS.)

Meiosis I

The four stages the meiosis Iare together follows, according to "Molecular biology of the Cell." (Garland Science, 2002):

Prophase I: in ~ this stage, chromosomes end up being compact, dense structures and are conveniently visible under the microscope. The homologous chromosomes pair together. The 2 sets the sister chromatids resemble two X"s lined up next to each other. Each collection exchanges bits that DNA through the other and also recombines, thus developing genetic variation. This procedure is recognized as crossing over, or recombination.

Even though in people the masculine sex chromosomes (X and Y) room not specific homologs, they can still pair together and also exchange DNA. Crossing over occurs within only a small an ar of the two chromosomes.

By the end of prophase I, the nuclear membrane breaks down.

Metaphase I: The meiotic spindle, a network the protein filaments, emerges from 2 structures called the centrioles, positioned in ~ either end of the cell. The meiotic spindle latches ~ above the unify sister chromatids. By the finish of metaphase I, every the unify sister chromatids room tethered at their centromeres and also line up in the center of the cell. The homologs still look favor two X"s sit close together.

Anaphase I: The spindle fibers start to contract, pulling the unify sister chromatids through them. Every X-shaped complex moves far from the other, toward opposite ends of the cell.

Telophase I: The fused sister chromatids with either finish of the cell, and the cell human body splits into two.

Meiosis I results in two daughter cells, each of which includes a collection of fused sister chromatids. The genetic makeup of every daughter cell is distinct due to the fact that of the DNA exchange between homologs during the crossing-over process.

Meiosis II

"Meiosis II looks like mitosis," Hoyt said Live Science. "It"s an equational division."

In other words, through the finish of the process, the chromosome number is unchanged between the cell that get in meiosis II and the resulting daughter cells.

The 4 stages that meiosis II are as follows, according to “Molecular biology of the Cell, fourth edition.”

Prophase II: The atom membrane disintegrates, and meiotic spindles begin to form once again.

Metaphase II: The meiotic spindles latch onto the centromere the the sister chromatids, and they every line up in ~ the center of the cell.

Anaphase II: The spindle fibers begin to contract and also pull the sisters chromatids apart. Each individual chromosome now begins to move to either end of the cell.

Telophase II: The chromosomes with opposite ends of the cell. The atom membrane creates again, and the cell human body splits right into two

Meiosis II outcomes in four haploid daughter cells, each with the same number of chromosomes. However, every chromosome is unique and contains a mix of genetic information indigenous the maternal and paternal chromosomes in the original parent cell.

Why is meiosis important?

Proper “chromosomal segregation,” or the separation the sister chromatids during meiosis I and II is important for generating healthy and balanced sperm and also egg cells, and also by extension, healthy and balanced embryos. If chromosomes fail come segregate completely, it"s dubbed nondisjunction and can an outcome in the formation of gametes the have lacking or extra chromosomes, follow to "Molecular biology of the Cell, 4th edition."

When gametes with abnormal chromosome numbers fertilize, most of the result embryos don"t survive. However, no all chromosomal abnormalities space fatalto the embryo. For example, down syndrome occurs as a result of having an extra copy of chromosome 21. And, people with Klinefelter syndromeare gene male yet have an extra X chromosome.

The most significant impact the meiosis is that it generates hereditary diversity, and that"s a major advantage for varieties survival.

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"Shuffling the hereditary information allows you to find new combinations i m sorry will probably be much more fit in the genuine world," Hoyt said.