Cell division - is a natural process, which ensures normal growth, development and reproduction of the organism.This increases the number of cells is carried out tissue growth, sexual reproduction and transmission of hereditary material.The main types of cell division - mitosis and meiosis is.Each of these processes has some peculiarities.
Mitosis
Mitosis - cell division is ultimately that of the mother cell is formed two subsidiaries with the same number and order of chromosomes.Similar processes occur constantly with somatic cells of the body, ensuring growth, development and regeneration of tissues and organs.
life cycle of cells can be divided into interphase and mitosis.Interphase - the so-called stage of calm, during which there is an active synthesis and accumulation necessary for cell division substances.Toward the beginning of mitosis occurs doubling the number of chromosomes.
Mitosis is usually divided into four main stages.
- Prophase.During this period, you will notice the beginning of chromosome condensation.Two identical chromosomes are interconnected one centromere.At the beginning of prophase is the division of the centrioles.Now two daughter centrioles begin slowly to disperse the two opposite sides of the cell.However, they remain bound by thin protein filaments - so formed division spindle.By the end of this stage, the chromosomes shorten and become much thicker and move to the equator of the cell.
- Metaphase - very short stage, which begins with the alignment of chromosomes at the equator of the cell.Around the same time, simultaneously in all the chromosomes is the division of the centromere.
- Anaphase - thread spindle is mounted in the centromere of the chromosome.During this period, the child slowly moving chromosomes to opposite poles.It is believed that the thread spindle is not only directed chromosomes, but also reduced due to the presence of ATP, accelerating their disagreement.
- Telophase - begins at the moment when the chromosomes had gone to the poles.They unwind and become less noticeable - return to a resting state.Around clusters of chromatin is a synthesis of a new nuclear envelope.In parallel with these is the division of cells - organelles and cytoplasm is evenly divided between affiliated entities.
Meiosis
Meiosis - a way of cell division, during which formed four gametes with a single set of chromosomes.Such processes take place during the formation of sex cells - sperm, eggs (the plant so the formation of spores).Such processes provide for the exchange of genetic material and combinatorial variability.When two gametes, each of which contains only half of the genetic material, the number of chromosomes is restored, but the sequence of changes.
process of gamete formation consists of two short meiotic divisions, each of which you can select all of the above stages.But between the two divisions have a pronounced interphase, and DNA synthesis occurs.Consequently, the second two cells enter the prophase with a single set of chromosomes (this is 46 in humans).The result of the second division - a 4 gametes which have 23 chromosomes.
amitosis
amitosis - is uncharacteristic cell division, which occurs rarely.In this cell maintains all physiological functions.During this process, there is no duplication of the genetic material, and cell division.Shares only the kernel, but without forming a spindle.As a result of this process the chromosomes disperse randomly - formed multinucleated cells.It is worth noting that amitosis usually meets or aging and dying cells, or in the pathologically altered structures (tumor cells).
