Typically, each cell in the human body has 46 chromosomes, including 22 pairs of autosomes and two sex chromosomes. Females have two X chromosomes, and males have one X chromosome and one Y chromosome.

The formation of the fetus's gender occurs at the moment the egg and sperm meet. According to the principle: an egg carrying the X chromosome meets a sperm carrying the X chromosome, forming an XX zygote – female gender. Conversely, an egg carrying the X chromosome meets a sperm carrying the Y chromosome, forming an XY zygote – male gender.