The process by which living organisms produce a new organism of their own kind is called reproduction. In humans, the first step in reproduction is called fertilization.
Fertilization takes place when the egg cell is joined by the sperm cell. They zygote that is formed has a complete set of chromosomes.
The zygote contains 46 chromosomes 23 from the father and 23 from the mother. The chromosomes are the carriers of the genes which are the determines of heredity. The genes are responsible for the differences in our appearance and intelligence.
The zygote stays in the uterus for 266 days or 38 weeks before it is born. The unborn is called fetus. The placenta supplies food and air to the unborn child.