You are watching: For a species with four pairs of chromosomes, ________ chromosome combinations are possible.
In general, this process involves a "parent" cell separating into 2 or an ext "daughter" cells. In this way, the parent cell can pass on its hereditary material from generation come generation.
eukaryotic bio cells and their chromosomes
Based top top the relative complexity of your cells, every living organisms are broadly classified as either prokaryotes or eukaryotes. Prokaryotes, such as bacteria, covers a solitary cell with a basic internal structure. Their DNA floats openly within the cabinet in a twisted, thread-like mass dubbed the nucleoid.
Animals, plants and fungi are all eukaryotes. Eukaryotic cells have devoted components dubbed organelles, such as mitochondria, chloroplasts and the absorbent reticulum. Each of this performs a certain function. Unequal prokaryotes, eukaryotic DNA is packed within a central compartment called the nucleus.
Within the eukaryotic bio nucleus, long double-helical strands the DNA are wrapped tightly roughly proteins referred to as histones. This develops a rod-like structure dubbed the chromosome.
Cells in the human body have 23 pairs of chromosomes, or 46 in total. This includes two sex chromosomes: 2 X chromosomes for females and also one X and also one Y chromosome because that males. Because each chromosome has a pair, these cells are called "diploid" cells.
On the various other hand, human spermand egg cells have only 23 chromosomes, or fifty percent the chromosomes the a diploid cell. Thus, lock are called "haploid" cells.
When the sperm and also egg combine during fertilization, the full chromosome number is restored. That"s since sexually reproducing organisms get a collection of chromosomes from each parent: a maternal and paternal set.Each chromosome has actually a corresponding pair, orhomolog.
Mitosis vs. Meiosis
Eukaryotesare qualified of two species of cell division: mitosisand meiosis
Mitosis permits for cells to create identical duplicates of themselves, which means the genetic material is duplicated from parental to daughter cells. Mitosis produces two daughter cell from one parent cell.
Single-celled eukaryotes, such as amoeba and also yeast, usage mitosis to reproduce asexuallyand rise their population. Multicell eukaryotes, favor humans, usage mitosis to prosper or heal injured tissues.
Meiosis, top top the various other hand, is a committed form the cell division that occurs in organisms the reproduce sexually. As discussed above, the produces reproductive cells, such as sperm cells, egg cells, and also spores in plants and fungi.
In humans, distinct cells dubbed 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 head chromosomes). Through the finish of meiosis, the resulting reproductive cells, orgametes, each have actually 23 genetically distinctive chromosomes.
The overall procedure of meiosis produces four daughter cells from one single parent cell. Every daughter cell is haploid, since it has half the number of chromosomes as the original parent cell.
"Meiosis is reductional," claimed M. Andrew Hoyt, a biologist and professor in ~ Johns Hopkins University.
Unlike in mitosis, the daughter cells produced during meiosis are genetically diverse. Homologous chromosomes exchange bits the DNA to create genetically unique, hybrid chromosomes destined because that each daughter cell.
A closer look in ~ meiosis
Before meiosis begins, some important changes take ar within the parent cells. First, each chromosome create a copy that itself. These replicated chromosomes are recognized as sister chromatids. They are fused together and the suggest where they are joined is recognized as the centromere. Fused sister chromatids around resemble the shape of the letter "X."
Meiosis occurs end the course of 2 rounds of atom divisions, called meiosis I and also meiosis II, follow to Nature Education"s Scitable. Furthermore, meiosis I and also II are each split into four major stages: prophase, metaphase, anaphase and telophase.
Meiosis ns is responsible for developing genetically distinctive chromosomes. Sister chromatids pair up v their homologs and also exchange hereditary material with one another. In ~ the end of this division, one parental cell produces 2 daughter cells, each transporting one set of sister chromatids.
Meiosis II carefully resembles mitosis. The 2 daughter cells move right into this phase without any type of further chromosome duplication. The sisters chromatids space pulled apart throughout this division. A complete of four haploid daughter cells are produced during the course of meiosis II.
Meiosis is the procedure whereby chromosomes are copied, paired up and separated to produce eggs or sperm. (Image credit: NIGMS.)
The four stages of meiosis Iare as follows, according to "Molecular biology of the Cell." (Garland Science, 2002):
Prophase I: at this stage, chromosomes end up being compact, dense structures and also are easily visible under the microscope. The homologous chromosomes pair together. The two sets the sister chromatids resemble two X"s lined up alongside each other. Each set exchanges bits the DNA through the other and also recombines, thus producing genetic variation. This procedure is recognized as cross over, or recombination.
Even though in human beings the male sex chromosomes (X and Y) are not exact homologs, they have the right to still pair together and also exchange DNA. Crossing over occurs within just a small region of the two chromosomes.
By the finish of prophase I, the atom membrane breaks down.
Metaphase I: The meiotic spindle, a network the protein filaments, emerges from 2 structures referred to as the centrioles, positioned in ~ either finish of the cell. The meiotic spindle latches onto the unify sister chromatids. By the finish of metaphase I, every the fused sister chromatids are tethered at their centromeres and line increase in the middle of the cell. The homologs still look choose two X"s sitting close together.
Anaphase I: The spindle fibers start to contract, pulling the unify sister chromatids through them. Each X-shaped facility moves far from the other, towards opposite ends of the cell.
Telophase I: The unify sister chromatids reach either finish of the cell, and also the cell body splits into two.
Meiosis I outcomes in two daughter cells, each of which contains a set of fused sister chromatids. The hereditary makeup of every daughter cabinet is distinct because of the DNA exchange in between homologs throughout the crossing-over process.
"Meiosis II looks choose mitosis," Hoyt said Live Science. "It"s an equational division."
In other words, by the finish of the process, the chromosome number is unchanged between the cell that get in meiosis II and also the resulting daughter cells.
The 4 stages of meiosis II room as follows, follow to “Molecular biologic of the Cell, fourth edition.”
Prophase II: The nuclear membrane disintegrates, and also meiotic spindles start to form once again.
Metaphase II: The meiotic spindles latch ~ above the centromere that the sister chromatids, and also they every 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 move to either end of the cell.
Telophase II: The chromosomes with opposite ends of the cell. The nuclear membrane develops again, and the cell body splits into two
Meiosis II results in 4 haploid daughter cells, each through the same variety of chromosomes. However, each chromosome is unique and also contains a mix of hereditary information native the maternal and also paternal chromosomes in the initial parent cell.
Why is meiosis important?
Proper “chromosomal segregation,” or the separation of sister chromatids throughout meiosis I and II is vital for generating healthy sperm and also egg cells, and by extension, healthy embryos. If chromosomes fail come segregate completely, it"s dubbed nondisjunction and also can an outcome in the development of gametes that have absent or extra chromosomes, follow to "Molecular biology of the Cell, fourth edition."
When gametes v abnormal chromosome numbers fertilize, many of the result embryos don"t survive. However, not all chromosomal abnormalities room fatalto the embryo. For example, down syndrome occurs as a an outcome of having an extra copy that chromosome 21. And, world with Klinefelter syndromeare gene male but have one extra X chromosome.
The most far-ranging impact of meiosis is the it generates genetic diversity, and also that"s a major advantage for species survival.
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"Shuffling the genetic information allows you come find new combinations i m sorry will perhaps be much more fit in the real world," Hoyt said.