You are watching: For a species with four pairs of chromosomes, ________ chromosome combinations are possible.
In general, this process involves a "parent" cell dividing into 2 or more "daughter" cells. In this way, the parental cell have the right to pass ~ above its hereditary material from generation to generation.
eukaryotic bio cells and also their chromosomes
Based on the relative complexity of their cells, every living biology are broadly classified together either prokaryotes or eukaryotes. Prokaryotes, such together bacteria, covers a single cell with a basic internal structure. Your DNA floats freely within the cell in a twisted, thread-like mass dubbed the nucleoid.
Animals, plants and fungi space all eukaryotes. Eukaryotic cells have specialized components called organelles, such as mitochondria, chloroplasts and the absorbent reticulum. Each of these performs a details function. Unlike prokaryotes, eukaryotic DNA is packed within a central compartment dubbed the nucleus.
Within the eukaryotic nucleus, long double-helical strands that DNA space wrapped tightly around proteins called histones. This creates a rod-like structure referred to as the chromosome.
Cells in the human being body have actually 23 pairs of chromosomes, or 46 in total. This has two sex chromosomes: two X chromosomes for females and also one X and also one Y chromosome for males. Because each chromosome has actually a pair, these cells are referred to as "diploid" cells.
On the other hand, human being spermand egg cells have only 23 chromosomes, or fifty percent the chromosomes that a diploid cell. Thus, lock are dubbed "haploid" cells.
When the sperm and also egg incorporate during fertilization, the complete chromosome number is restored. That"s since sexually reproducing organisms get a set of chromosomes from each 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 allows for cell to create identical duplicates of themselves, which way the genetic material is copied from parental to daughter cells. Mitosis produces two daughter cells from one parent cell.
Single-celled eukaryotes, such as amoeba and also yeast, usage mitosis come reproduce asexuallyand rise their population. Multicellular eukaryotes, like humans, use mitosis to thrive or heal injured tissues.
Meiosis, top top the various other hand, is a dedicated form the cell department that occurs in organisms the reproduce sexually. As pointed out above, the produces reproductive cells, such together sperm cells, egg cells, and also spores in plants and also fungi.
In humans, special cells referred to as germ cells undergo meiosis and ultimately provide rise come sperm or eggs. Germ cell contain a complete collection of 46 chromosomes (23 maternal chromosomes and 23 paternal chromosomes). By the end of meiosis, the resulting reproductive cells, orgametes, each have actually 23 genetically distinct chromosomes.
The overall process of meiosis produces 4 daughter cells from one single parent cell. Every daughter cell is haploid, because it has fifty percent the number 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 developed during meiosis are genetically diverse. Homologous chromosomes exchange bits of DNA to develop genetically unique, hybrid chromosomes destined for each daughter cell.
A closer look in ~ meiosis
Before meiosis begins, part important changes take ar within the parental cells. First, every chromosome creates a copy that itself. These duplicated chromosomes are known as sister chromatids. They space fused together and the allude where they are joined is recognized as the centromere. Fused sister chromatids approximately resemble the form of the letter "X."
Meiosis occurs over the course of 2 rounds of atom divisions, dubbed meiosis I and also meiosis II, follow to Nature Education"s Scitable. Furthermore, meiosis I and II are each divided into four major stages: prophase, metaphase, anaphase and also telophase.
Meiosis i is responsible for developing genetically distinctive chromosomes. Sister chromatids pair up through their homologs and also exchange hereditary material through one another. In ~ the end of this division, one parent cell produces 2 daughter cells, each moving one set of sisters chromatids.
Meiosis II very closely resembles mitosis. The 2 daughter cell move into this phase without any type of further chromosome duplication. The sister chromatids are pulled apart throughout this division. A total of four haploid daughter cell are produced during the course of meiosis II.
Meiosis is the procedure whereby chromosomes room copied, paired up and also separated to create eggs or sperm. (Image credit: NIGMS.)
The four stages that meiosis Iare together follows, according to "Molecular biologic of the Cell." (Garland Science, 2002):
Prophase I: at this stage, chromosomes come to be compact, thick structures and also are easily visible under the microscope. The homologous chromosomes pair together. The two sets the sister chromatids resemble two X"s inside wall up next to each other. Each collection exchanges bits of DNA v the other and recombines, thus developing genetic variation. This procedure is known as crossing over, or recombination.
Even despite in human beings the masculine sex chromosomes (X and also Y) space not exact homologs, they can still pair together and also exchange DNA. Crossing over occurs within just a small region of the two chromosomes.
By the end of prophase I, the atom membrane division down.
Metaphase I: The meiotic spindle, a network the protein filaments, increase from 2 structures dubbed the centrioles, positioned in ~ either end of the cell. The meiotic spindle latches top top the fused sister chromatids. By the end of metaphase I, every the unify sister chromatids room tethered at your centromeres and line up in the center of the cell. The homologs quiet look like two X"s sitting close together.
Anaphase I: The spindle fibers start to contract, pulling the fused sister chromatids through them. Each X-shaped complex moves far from the other, toward opposite end of the cell.
Telophase I: The unify sister chromatids reach either end of the cell, and also the cell body splits into two.
Meiosis I outcomes in two daughter cells, each of which contains a collection of fused sister chromatids. The genetic makeup of each daughter cell is distinct since of the DNA exchange in between homologs throughout the crossing-over process.
"Meiosis II looks like mitosis," Hoyt called Live Science. "It"s an equational division."
In other words, by the end of the process, the chromosome number is unchanged between the cells that go into meiosis II and the resulting daughter cells.
The four stages the meiosis II room as follows, according to “Molecular biology of the Cell, 4th edition.”
Prophase II: The nuclear membrane disintegrates, and also meiotic spindles start to kind once again.
Metaphase II: The meiotic spindles latch top top the centromere the the sisters chromatids, and they every line up in ~ the facility of the cell.
Anaphase II: The spindle fibers start to contract and pull the sister chromatids apart. Every individual chromosome now starts to moves to either finish of the cell.
Telophase II: The chromosomes with opposite end of the cell. The atom membrane develops again, and also the cell body splits into two
Meiosis II outcomes in 4 haploid daughter cells, each with the same variety of chromosomes. However, every chromosome is unique and also 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 also II is essential 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 result in the formation of gametes the have missing or extra chromosomes, according to "Molecular biology of the Cell, fourth edition."
When gametes through abnormal chromosome numbers fertilize, most of the resulting embryos don"t survive. However, no all chromosomal abnormalities space fatalto the embryo. Because that example, under syndrome occurs together a result of having an extra copy of chromosome 21. And, world with Klinefelter syndromeare genetically male but have an extra X chromosome.
The most significant impact of meiosis is that it generates genetic diversity, and that"s a major advantage for types survival.
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"Shuffling the hereditary information enables you to find new combinations which will possibly be an ext fit in the actual world," Hoyt said.