During Meiosis 2 Chromosomes Line Up Again Along the Cell
What Is Meiosis?
All cells arise from other cells through the process of prison cell division. Meiosis is a specialized form of jail cell division that produces reproductive cells, such equally plant and fungal spores and sperm and egg cells.
In general, this process involves a "parent" jail cell splitting into two or more "daughter" cells. In this style, the parent cell can pass on its genetic fabric from generation to generation.
Eukaryotic cells and their chromosomes
Based on the relative complication of their cells, all living organisms are broadly classified as either prokaryotes or eukaryotes. Prokaryotes, such equally leaner, consist of a unmarried cell with a elementary internal structure. Their DNA floats freely within the cell in a twisted, thread-like mass called the nucleoid.
Animals, plants and fungi are all eukaryotes. Eukaryotic cells have specialized components called organelles, such every bit mitochondria, chloroplasts and the endoplasmic reticulum. Each of these performs a specific part. Unlike prokaryotes, eukaryotic Dna is packed inside a central compartment chosen the nucleus.
Inside the eukaryotic nucleus, long double-helical strands of Dna are wrapped tightly around proteins chosen histones. This forms a rod-like construction called the chromosome.
Cells in the homo body take 23 pairs of chromosomes, or 46 in total. This includes ii sex activity chromosomes: ii X chromosomes for females and one X and one Y chromosome for males. Considering each chromosome has a pair, these cells are chosen "diploid" cells.
On the other hand, man sperm and egg cells have only 23 chromosomes, or half the chromosomes of a diploid cell. Thus, they are called "haploid" cells.
When the sperm and egg combine during fertilization, the total chromosome number is restored. That'due south considering sexually reproducing organisms receive a set of chromosomes from each parent: a maternal and paternal set. Each chromosome has a corresponding pair, orhomolog.
Mitosis vs. meiosis
Eukaryotes are capable of 2 types of jail cell division: mitosis and meiosis
Mitosis allows for cells to produce identical copies of themselves, which means the genetic material is duplicated from parent to daughter cells. Mitosis produces two daughter cells from one parent cell.
Single-celled eukaryotes, such every bit amoeba and yeast, use mitosis to reproduce asexuallyand increase their population. Multicellular eukaryotes, similar humans, use mitosis to grow or heal injured tissues.
Meiosis, on the other hand, is a specialized form of cell sectionalization that occurs in organisms that reproduce sexually. As mentioned above, information technology produces reproductive cells, such as sperm cells, egg cells, and spores in plants and fungi.
In humans, special cells chosen germ cells undergo meiosis and ultimately give rise to sperm or eggs. Germ cells comprise a complete set of 46 chromosomes (23 maternal chromosomes and 23 paternal chromosomes). Past the end of meiosis, the resulting reproductive cells, or gametes, each have 23 genetically unique chromosomes.
The overall process of meiosis produces four girl cells from one single parent cell. Each daughter cell is haploid, because it has half the number of chromosomes equally the original parent prison cell.
"Meiosis is reductional," said M. Andrew Hoyt, a biologist and professor at Johns Hopkins University.
Different in mitosis, the girl cells produced during meiosis are genetically various. Homologous chromosomes exchange bits of Deoxyribonucleic acid to create genetically unique, hybrid chromosomes destined for each daughter cell.
A closer await at meiosis
Earlier meiosis begins, some important changes take place within the parent cells. Commencement, each chromosome creates a copy of itself. These duplicated chromosomes are known every bit sis chromatids. They are fused together and the indicate where they are joined is known equally the centromere. Fused sister chromatids roughly resemble the shape of the letter of the alphabet "X."
Meiosis occurs over the grade of two rounds of nuclear divisions, called meiosis I and meiosis II, according to Nature Didactics's Scitable. Furthermore, meiosis I and II are each divided into iv major stages: prophase, metaphase, anaphase and telophase.
Meiosis I is responsible for creating genetically unique chromosomes. Sis chromatids pair upwardly with their homologs and exchange genetic material with one some other. At the end of this division, i parent cell produces two daughter cells, each conveying i set of sister chromatids.
Meiosis Two closely resembles mitosis. The two daughter cells motility into this stage without any further chromosome duplication. The sister chromatids are pulled apart during this division. A total of iv haploid girl cells are produced during the course of meiosis II.
Meiosis I
The four stages of meiosis Iare as follows, according to "Molecular Biological science of the Cell." (Garland Science, 2002):
Prophase I: At this stage, chromosomes get meaty, dense structures and are easily visible nether the microscope. The homologous chromosomes pair together. The two sets of sis chromatids resemble two X'due south lined up next to each other. Each fix exchanges bits of Deoxyribonucleic acid with the other and recombines, thus creating genetic variation. This process is known every bit crossing over, or recombination.
Even though in humans the male sex activity chromosomes (X and Y) are not exact homologs, they can notwithstanding pair together and exchange Deoxyribonucleic acid. Crossing over occurs within only a small region of the two chromosomes.
Past the end of prophase I, the nuclear membrane breaks down.
Metaphase I: The meiotic spindle, a network of protein filaments, emerges from two structures called the centrioles, positioned at either end of the cell. The meiotic spindle latches onto the fused sister chromatids. By the finish of metaphase I, all the fused sister chromatids are tethered at their centromeres and line up in the middle of the cell. The homologs however look like two X's sitting close together.
Anaphase I: The spindle fibers start to contract, pulling the fused sister chromatids with them. Each X-shaped complex moves away from the other, toward contrary ends of the cell.
Telophase I: The fused sister chromatids reach either finish of the cell, and the cell body splits into two.
Meiosis I results in two daughter cells, each of which contains a ready of fused sis chromatids. The genetic makeup of each daughter cell is distinct because of the DNA exchange between homologs during the crossing-over procedure.
Meiosis II
"Meiosis II looks like mitosis," Hoyt told Live Science. "It's an equational division."
In other words, by the finish of the process, the chromosome number is unchanged betwixt the cells that enter meiosis II and the resulting daughter cells.
The 4 stages of meiosis II are as follows, according to "Molecular Biology of the Prison cell, 4th edition."
Prophase Two: The nuclear membrane disintegrates, and meiotic spindles begin to form in one case once again.
Metaphase Two: The meiotic spindles latch onto the centromere of the sister chromatids, and they all line up at the center of the cell.
Anaphase Ii: The spindle fibers start to contract and 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 forms once more, and the cell body splits into two
Meiosis 2 results in four haploid daughter cells, each with the aforementioned number of chromosomes. However, each chromosome is unique and contains a mix of genetic data from the maternal and paternal chromosomes in the original parent cell.
Why is meiosis important?
Proper "chromosomal segregation," or the separation of sister chromatids during meiosis I and Ii is essential for generating good for you sperm and egg cells, and by extension, healthy embryos. If chromosomes fail to segregate completely, it'due south chosen nondisjunction and can upshot in the formation of gametes that have missing or extra chromosomes, co-ordinate to "Molecular Biology of the Jail cell, 4th edition."
When gametes with aberrant chromosome numbers fertilize, almost of the resulting embryos don't survive. Nevertheless, non all chromosomal abnormalities are fatal to the embryo. For example, Down's syndrome occurs as a issue of having an extra copy of chromosome 21. And, people with Klinefelter syndrome are genetically male but have an extra 10 chromosome.
The most significant impact of meiosis is that information technology generates genetic variety, and that'due south a major reward for species survival.
"Shuffling the genetic information allows you to find new combinations which will maybe be more than fit in the existent world," Hoyt said.
Source: https://www.livescience.com/52489-meiosis.html
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