Cell division is a natural process that ensures the normal growth, development and reproduction of the body. Due to this, the number of cells increases, tissue growth, sexual reproduction and transmission of hereditary material is carried out. The main types of cell division are meiosis and mitosis. Each of these processes has some features.
Mitosis
Mitosis is cell division, in the end of which two daughter cells with the same number and order of chromosomes are formed from the mother cell. Similar processes constantly occur with somatic cells of the body, providing growth, development, regeneration of tissues and organs.
The cell life cycle can be divided into interphase and mitosis. Interphase is the so-called calm stage, during which there is an active synthesis and accumulation of substances necessary for cell division. Closer to the onset of mitosis, the number of chromosomes doubles.
Mitosis is usually divided into four main stages.
- Prophase. During this period, you can notice the beginning of the condensation of chromosomes. Two identical chromosomes are interconnected by one centromere. At the beginning of prophase, centriole division occurs. Now the two daughter centrioles begin to slowly diverge towards the two opposite sides of the cell. At the same time, they remain connected by thin protein threads - this is how the division spindle is formed. By the end of this stage, the chromosomes are greatly shortened and become thicker and move to the equator of the cell.
- Metaphase is a very short stage, which begins with the alignment of chromosomes at the equator of the cell. At about the same time, centromere division occurs on all chromosomes simultaneously.
- Anaphase - the thread of the fission spindle is attached to the centromere of the chromosome. During this period, daughter chromosomes slowly move to opposite poles. It is believed that the threads of the fission spindle not only direct the chromosomes, but also due to the presence of ATP are reduced, accelerating their divergence.
- Telophase - begins at the moment when the chromosomes have already dispersed to the poles. They unwind and become less noticeable - they return to a state of rest. Around the accumulation of chromatin, a new nuclear envelope is synthesized. In parallel with these, cell division occurs - the cytoplasm and organelles are equally divided between daughter structures.
Meiosis
Meiosis is a method of cell division during which four gametes with a single set of chromosomes are formed. Such processes occur during the formation of germ cells - spermatozoa, eggs (the plant thus forms spores). Similar processes provide the exchange of genetic material and combinatorial variability. When two gametes merge, each of which contains only half of the genetic material, the number of chromosomes is restored, but their sequence changes.
The gamete formation process consists of two short meiotic divisions, in each of which all the above stages can be distinguished. But between the two divisions there is no pronounced interphase, and DNA synthesis does not occur. Therefore, two cells with a single set of chromosomes enter the second prophase (in humans this is 46). The result of the second division is 4 gametes that have 23 chromosomes each.
Amitosis
Amitosis is an uncharacteristic cell division that is observed quite rarely. In this case, the cell retains all physiological functions. During this process, there is no doubling of genetic material and cell division. Only the core is divided, but without the formation of a fission spindle. As a result of this process, the chromosomes diverge in random order - a multinuclear cell is formed. It is worth noting that amitosis, as a rule, occurs either in aging and dying cells, or in pathologically altered structures (tumor cells).