Some creatures, such as amoeba, are reproduced simply by dividing it in half. This is very convenient! But the offspring resulting is quite predictable. One amoeba can produce infinitely many of its reproductions, but they will all be identical to the first. Sexual reproduction, on the contrary, gives an almost unlimited variety, since the characteristics of the offspring are a disorderly mixture of properties and features of its ancestors from the family trees of both parents. Some have some talents, others manage to combine a lot of talents - all this helps such a complex creature as a person to survive in our world, which makes serious demands.
Each cell of the human body contains a "set" of information on the basis of which it was built. This information is stored in 23 pairs of chromosomes located in the cell nucleus. Chromosomes determine the production of proteins - the main building material: what proteins the cell produces, when and how. This in turn determines the characteristics and activity of the cell.
When a cell divides to provide body growth, pairs of chromosomes are duplicated before division. This means that the same 23 pairs of new chromosomes are produced, and they carry exactly the same information as the old chromosomes. But when the body produces cells for sexual reproduction, it divides the cells without prior duplication of chromosomes. The vapors diverge, and each sex cell receives only 23 separate chromosomes, one from each pair. Thus, each of these cells receives only half of the information contained in a normal cell. The sperm cell is the male version of such cells, and the egg cell is female. When the sperm and the egg join, a new fertilized egg (zygote), from which the fetus grows, again contains 23 pairs of chromosomes - half of each parent.