Sexual reproduction

Article

July 5, 2022

Sexual reproduction is the formation of a new organism with the participation of two parental organisms.

Essence

During sexual reproduction, the fusion of sex cells — gametes of the male and female organism — takes place. The new organism contains the hereditary information of both parents. Germ cells are formed as a result of a special type of division, in which the number of chromosomes in cells formed as a result of division is half that of the original mother cell. Thus, gametes have half the number of chromosomes. As a result of the fusion of two gametes, the number of chromosomes in the newly formed cell doubles, that is, it is restored, and one half of all chromosomes is paternal, the other - maternal. Types of sexual reproduction are parthenogenesis and self-fertilization. In higher plants and vertebrates, the female reproductive cell - the egg cell - is immobile, it is larger than male gametes, as it contains a supply of nutrients. Male gametes are spermatozoa in animals and spermatozoa in plants.

Development of germ cells in animals

The development of germ cells is called gametogenesis. It consists of the following stages[source?]: Breeding period Cells divide by mitosis. As a result, the number of cells increases, all of them contain a diploid set of chromosomes (2n). Male cells are called spermatogonia, and female cells are called oogonia. Growth period The cells increase in size and are called spermatocytes of the first order or oocytes of the first order. This period is especially well expressed in eggs, in which spare nutrients accumulate. Ripening period During this period, meiosis occurs. In males, 4 haploid cells - spermatids - are formed. In the female body, 3-4 cells are formed - one egg cell and 2-3 small cells - polar bodies, which die. This happens because, from an evolutionary point of view, it turned out to be more profitable to concentrate the supply of nutrients in one, and not in 4 cells. Formative period Mature gametes are formed - 4 sperm and one egg. After the fusion of the gametes, a diploid zygote is formed, which carries hereditary information from both parents. In this way, the main purpose of sexual reproduction is ensured - recombination�