All cells arise from other cells v the procedure of cell division. Meiosis is a dedicated form of cell division that produces reproductive cells, such together plant and fungal spores and also sperm and also egg cells.

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In general, this process involves a "parent" cell separating into 2 or more "daughter" cells. In this way, the parental cell can pass ~ above its hereditary material indigenous generation to generation.

eukaryotic bio cells and their chromosomes

Based on the relative intricacy of your cells, every living biology are broadly classified as either prokaryotes or eukaryotes. Prokaryotes, such together bacteria, consists a solitary cell through a an easy 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 specialized components referred to as organelles, such as mitochondria, chloroplasts and the endoplasmic reticulum. Each of these performs a details function. Uneven prokaryotes, eukaryotic bio DNA is packed in ~ a main compartment called the nucleus.


Within the eukaryotic nucleus, lengthy double-helical strands that DNA space wrapped tightly approximately proteins referred to as histones. This forms a rod-like structure referred to as the chromosome.


Cells in the person body have 23 pairs of chromosomes, or 46 in total. This contains two sex chromosomes: two X chromosomes because that females and also one X and one Y chromosome for males. Since each chromosome has a pair, this cells are called "diploid" cells.

On the other hand, human spermand egg cells have only 23 chromosomes, or fifty percent the chromosomes of a diploid cell. Thus, lock are dubbed "haploid" cells.

When the sperm and also egg combine during fertilization, the full chromosome number is restored. That"s because sexually reproducing organisms receive a collection of chromosomes from every parent: a maternal and also paternal set.Each chromosome has a matching pair, orhomolog.


Mitosis vs. Meiosis

Eukaryotesare qualified of two types of cell division: mitosisand meiosis

Mitosis enables for cells to develop identical duplicates of themselves, which means the genetic material is copied from parental to daughter cells. Mitosis produces two daughter cells from one parent cell.

Single-celled eukaryotes, such together amoeba and also yeast, usage mitosis to reproduce asexuallyand increase their population. Multicellular eukaryotes, prefer humans, usage mitosis to thrive or heal hurt tissues.

Meiosis, top top the other hand, is a committed form of cell department that wake up in organisms the reproduce sexually. As discussed above, that produces reproductive cells, such together sperm cells, egg cells, and also spores in plants and also fungi.

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

The overall process of meiosis produces four daughter cell from one solitary parent cell. Every daughter cell is haploid, due to the fact that it has fifty percent the variety of chromosomes together the initial parent cell.

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

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

A closer look at meiosis

Before meiosis begins, some important transforms take place within the parental cells. First, every chromosome creates a copy the itself. These replicated chromosomes are well-known as sister chromatids. They space fused together and also the suggest where they space joined is recognized as the centromere. Fused sister chromatids about resemble the form of the letter "X."

Meiosis occurs over the food of 2 rounds of atom divisions, called meiosis I and meiosis II, according to Nature Education"s Scitable. Furthermore, meiosis I and II are each separated into four significant stages: prophase, metaphase, anaphase and telophase.

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

Meiosis II very closely resembles mitosis. The two daughter cell move right into this phase without any further chromosome duplication. The sister chromatids space pulled apart throughout this division. A total of four haploid daughter cell are produced during the food of meiosis II.


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Meiosis is the process whereby chromosomes are copied, combine up and also separated to develop eggs or sperm. (Image credit: NIGMS.)

Meiosis I

The 4 stages the meiosis Iare together follows, according to "Molecular biologic of the Cell." (Garland Science, 2002):

Prophase I: at this stage, chromosomes end up being compact, dense structures and are easily visible under the microscope. The homologous chromosomes pair together. The two sets the sister chromatids resemble two X"s lined up next to each other. Each set exchanges bits the DNA through the other and also recombines, thus creating genetic variation. This process is known as crossing over, or recombination.

Even despite in humans the masculine sex chromosomes (X and Y) space not exact homologs, they have the right to still pair together and also exchange DNA. Crossing end occurs within just a small region 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, increase from 2 structures referred to as the centrioles, positioned at either finish of the cell. The meiotic spindle latches top top the fused sister chromatids. Through the end of metaphase I, every the fused sister chromatids room tethered at their centromeres and also line up in the center of the cell. The homologs quiet look prefer two X"s sit close together.

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

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

Meiosis I outcomes in 2 daughter cells, each of which includes a set of fused sister chromatids. The genetic makeup of each daughter cabinet is distinct because of the DNA exchange between homologs during the crossing-over process.

Meiosis II

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

In various other words, by the finish of the process, the chromosome number is unchanged in between the cells that enter meiosis II and the result daughter cells.

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

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

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

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

Telophase II: The chromosomes reach opposite ends of the cell. The nuclear membrane creates again, and also the cell body splits into two

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

Why is meiosis important?

Proper “chromosomal segregation,” or the separation of sister chromatids throughout meiosis I and II is necessary for generating healthy and balanced sperm and also egg cells, and also by extension, healthy and balanced embryos. If chromosomes fail to segregate completely, it"s referred to as nondisjunction and also can an outcome in the development of gametes that have lacking or extra chromosomes, according to "Molecular biologic of the Cell, fourth edition."

When gametes through abnormal chromosome numbers fertilize, many of the result embryos don"t survive. However, not all chromosomal abnormalities room fatalto the embryo. Because that example, under syndrome occurs as a an outcome of having actually an extra copy of chromosome 21. And, human being with Klinefelter syndromeare genetically male yet have one extra X chromosome.

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

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"Shuffling the hereditary information enables you to find brand-new combinations i beg your pardon will perhaps be more fit in the actual world," Hoyt said.