Final answer:
When a sperm penetrates the egg, its nucleus fuses with the nucleus of the egg, resulting in a cell called a zygote.
Step-by-step explanation:
When a sperm penetrates the egg, it triggers the egg to complete meiosis. The sperm also undergoes changes. Its tail falls off, and its nucleus fuses with the nucleus of the egg. The resulting cell, called a zygote, contains all the chromosomes needed for a new human organism. Half the chromosomes come from the egg and half from the sperm.