Fertilization. The appearance of twins

Fertilization

During the sexual intercourse of the sperm (about 200 million) in the vagina and move towards the uterus. For a few hours, the spermatozoa reaches the fallopian tube, where they can meet the egg. In the uterine tube there is a fertilization process.

Fertilization is the process of fusion of the sperm and egg cell, as a result of which the zygote is formed.
The floor of the future person is determined at the time of fertilization and depends on what spermatozoa is fertilized by an egg. In cells there are storage media – chromosome. All egg cells contain chromosome X. Half of the spermatozoa contains chromosome X, and the other half contains chromosome Y. If the egg fertilizes the X-containing spermatozoa, a girl will appear; If Y-containing – a boy will be born.

Fertilization is possible for 12-24 hours after ovulation (since during this period the egg retains its viability). The ability to fertilize in spermatozoa is preserved from 2 to 4 days.

The process of fertilization itself occurs as follows. Sperm climbs are approaching the egg, come into contact with its shells and excrete an enzyme that disrupts the integrity of the egg shells. Usually in the egg penetrates and merges with it only one spermatozoa. After that, a special shell is formed around the egg that impede the penetration of other spermatozooid nuclei into it.

Twins

When ovulation and fertilization of two (or more) eggs are formed two or more fetus. These are future diverse twins. They are not very similar to each other and can even be a different floor.

If two fetus develop from one egg cell, then these are single-time twins. They are always one sex and are very similar to each other.