division is not only the key to restoring the integrity of tissues and reproduction of organisms.In itself, cell division involves the formation of two or more daughter cells from a single parent.Chromosomes occupy a very important place in the process of cell division.It is they who are responsible for the transmission of information between the generations.
cell division.Mitosis and meiosis
There are two main types of division - mitosis and meiosis.The first involves the formation of a single parent of two daughter cells.The number of chromosomes in both cells is the same as in the parent cell, i.e. the cells are identical.Increasing the number of chromosomes occurs before division.Thus, the cell turns from diploid to tetraploid.Upon completion of formation of two diploid cells.
called meiosis formation of four cells.Thus each of these chromosomes twice smaller than the parent.Meiosis often occurs immediately after the first division.As a result, one gets four haploid diploid.
between cell division should grow and develop in preparation for the new division.During this time it accumulates a lot of protein and also doubled the most important organelles, and with them, and chromosomes.
accepted to distinguish four phases of mitosis, which follow each other and continue up to two hours.Mitotic cell division involves the following steps.
At the first stage the centrioles move away to the poles of the cell.Thereafter, formed spindle.Chromosomes become more visible.This dissolves the nuclear membrane and nucleolus disappear below.
second stage of division is that the chromosomes have to stay along the equator and the cells attached to the spindle of division.
In the third stage the chromosomes or chromatids children begin the process of divergence to the poles of the cell due to the spindles.
The next step disappear spindle, around the already dispersed chromosomes begin to form the nuclear envelope.After that divides the cytoplasm and daughter cells are formed.Since cell division occurs.
Meiosis Meiosis is most often associated with sexual reproduction of cells and the formation of sex cells in fungi, plants and animals.Cell division is divided into two successive processes of division, but doubling the chromosomes occurs just before the first division.That is why the resulting cell contains half the number of chromosomes.The process of meiosis consists of two main stages - before division before the division, each of which is divided into separate stages.
the first stage before the division of chromosomes is well marked.Thus homologous chromosomes begin to form a pair of tightly adhering to each other, and then twisting along its entire length.Thereafter, homologous regions of the chromosomes are exchanged portions to each other and separated.Next homologous chromosomes must line up at the equator.In the next step the chromosome, which consist of two chromatids begin to diverge toward the poles.The discrepancy of each pair is independent of the other pairs of chromosomes divergence.So formed daughter cells with half the number of chromosomes.
second cell division.The first phase involves the destruction of the nuclear envelope and the disappearance of the nucleolus.After that appear spindle.Then, the chromosomes must line up at the equator, attaching the spindle.In the third stage both chromatids daughter cells gradually diverge to the poles.Then there are cells with a single set of chromosomes.Then they form germ cells.After the merger, the number of germ cell chromosomes in the new cell is restored.
