Reproduction of organisms

One of the main characteristics of the animal organism – the ability to grow or reproduce.
In multicellular animal organisms cells multiply over a lifetime by fission, or mitosis (karyokinesis). After mitosis in each daughter cell remains the same number of chromosomes (diploid chromosomes) of the same type as in the parent cell.
In the developing germ cells after two successive divisions during which the chromosomes are split longitudinally only once, there is a reduction in the number of chromosomes by half (haploid set of chromosomes). This division is called meiosis. During the multiplication of the merger of sperm and egg cells, in which there is a haploid set of chromosomes in the cells of the fruit is reduced to a set of diploid chromosomes.

After meiosis in all egg cells of women in the 23rd pair of chromosomes contains X chromosomes, while men in the same half of the sperm contains the X chromosome and the other – the Y-chromosome. If the egg cell is fertilized by a sperm with the X chromosome, then it develops a girl, but because of the egg cells, fertilized the Y chromosome, the boy develops.
The function of reproduction is regulated by the nervous system and the products of the endocrine glands – hormones.
As a result of the breeding parents pass on to descendants hereditary information, providing them the ability to survive in a particular environment, and produce offspring. During the multiplication of the conditions for the occurrence of changes in the properties of organisms through the exchange of hereditary factors specific to parents. Reproduction ensure the continued existence of different kinds of time, evolutionary processes and the “immortality” of life on Earth (since its inception).
On Earth organisms distinguish two fundamentally different from other forms of reproduction: asexual and sexual.


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Reproduction of organisms