Four split

The four split refers to the first division of the animal cell meiosis (minus I) in early two, has been self replicating Homologous chromosomes The Federation The formation of four Chromatid Combination
Four split

Four split The four split (tetrad)

The four split refers to the first division of the animal cell meiosis (minus I) of the early two have complex self
 Homologous chromosome crossover (homologous chromosome synapsis) Homologous chromosome crossover (homologous chromosome synapsis)
System Homologous chromosomes The Federation The formation of four Chromatid Combination.
The other plant stamens in the direction of differentiation of the megaspore mother cell division, before the formation, structure of four pollen callose formation by.

Four split Definition

In meiosis, the homologous chromosome synapsis, so that each pair of homologous chromosomes containing four chromatids, then a pair of homologous chromosomes is also called a split four.
stay Meiosis In four, the body is electron microscope Primary germ cell A visible stage. At this stage Primary spermatocyte and Primary oocytes In the same shape and size, a father of a chromosome called from the maternal side Homologous chromosomes . 22 pairs of homologous chromosomes, because each chromosome contains two Sister chromatid Therefore,, after pairing each pair of homologous chromosomes contain four chromatids, called four split.
Four points each have 2 chromosomes, 2 pairs (4) sister chromatids, 1 pairs of chromosomes, 4 monomer, 4 DNA molecules. Because Four split period Between homologous chromosomes often intertwined, and then separately can not maintain the chromosome morphology and composition of the original, possible non homologous Sister chromosome Between crossing over This is, chromatid and chromosome, soon after Gene recombination The reason. In Botany, there is a four split concept, refers to the anther development to a certain stage, the formation contains four small Spore The Pollen mother cell . The meiosis of pollen mother cells was divided into four, four points of further development and maturation after the release of 4 mature pollen grains.
Four body is 2 times of that body sexual reproduction Biological cell meiosis I Prophase ( Zygotene Two) homologous chromosome synapsis formation complex, because there are 4 chromatids and is called the four divided body.
The best period in the observation of meiotic division is diplotene.

Four split The meiosis

Four split The process of meiosis

Note: meiosis can be divided into two stages, interval and Split phase Among them, mitosis is divided into meiosis stage (minus one), second division (meiosis period minus two).
The 1 cell division before the interval, DNA and the replication of chromosomes, chromosome number unchanged, the number of DNA is two times the original cell.
2 minus one early Homologous chromosomes The Federation Form four (or split " Two of the body "), appeared spindle, nucleolus The nuclear membrane disappeared.
3 minus one homologous chromosome metaphase. Centromere In the symmetrical arrangement Equatorial plate Both ends。 (and animal cell mitosis is roughly the same as that of animal cell mitotic kinetochores are arranged on the equatorial plate)
4 minus one later, the separation of homologous chromosomes, chromosome free combination, move to the cell poles.
5 minus one end cell One divides into two., formed the secondary spermatocyte or the formation of the secondary oocyte and The first polar body .
6 minus two early secondary spermatocyte chromosome gathered again again Spindle .
7 minus two metaphase chromosome centromere in Equatorial plate On.
8 minus two chromosome centromere separation, chromosome shift The poles .
9 by the end of two One divides into two. cells, Spermatogonial cells formation Sperm cells , Ovogonium formation Egg cell And second Polar body .

Four split Biological significance

Meiosis is the basis of genetics. Specific performance in:
1 in the meiosis process, because of the separation of homologous chromosomes, respectively in different Sub cell Therefore, in the sub cell having only one chromosome of each pair of homologous chromosomes. meiosis Homologous chromosomes The separation is the cytological basis of gene separation law.
2 homologous chromosome synapsis and four split period exchange segments may be non symmetry between the monomer sister chromosome position, which is between paternal and maternal chromosome genetic material The exchange. This exchange can make chromosome linkage with gene recombination, which is on the chromosome Gene linkage The cellular basis and exchange.
Because of meiosis, so that each species of generations are able to maintain the diploid number of chromosomes. In the process of meiosis chromosome re combination of homologous chromosome exchange occurred, the genetic basis of gamete diversification, the offspring of the changes in environmental conditions have greater adaptability.
1 to ensure the stability of sexual reproduction of individual organisms and generations through meiotic chromosome number of cells (gametes) led to the halving of chromosome number, 2n chromosomes from somatic cells into gametes n chromosomes, after sexual gametes, zygote chromosome number and return to the parental 2n level, the sexual reproduction of the offspring chromosome number of parents always keep inherent, ensure the relative stability of genetic material.
The 2 is in the process of sexual reproduction creation provides the material basis of genetic variation:
By 1 Non homologous chromosomes The combination of the random; non homologous chromosomes in free combination into gametes, formation of gametes can produce a variety of genetic combinations, with male and female gametes can occur after individual variation varied, the species will survive and evolve, provide abundant material for natural selection.
Through the exchange of 2 non sister chromatid fragments in pachytene meiosis stage, due to the non sister chromatid exchange may occur on the corresponding fragment, the homologous genetic material on chromosome recombination, genetic variation is different from the parent form.