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Fertilization is the union of sex cells (sperm and egg) that takes place in one of the fallopian tubes.
During intercourse, when ejaculation occurs the semen is deposited in the bottom of the vagina. Thousands of sperm die at this stage. The survivors go up through the uterus and head to the fallopian tubes.
Some of these sperm get close to the egg, although only one will penetrate it. The egg creates a barrier around itself preventing any other sperm from entering it.
At this time, the two genetic codes (female and male) come into contact. Thus, the zygote, which is surrounded by nutrients, is formed in the tube.
