Final answer:
The sperm's tail falls off after it penetrates the egg and the nuclei fuse to form a zygote with complete chromosomes for a new human.
Step-by-step explanation:
Upon fertilization, when a sperm penetrates the egg, several changes occur. The tail of the sperm, which provided the motility necessary for it to reach the egg, is no longer needed and therefore falls off.
Once the sperm's nucleus enters the egg, it fuses with the egg's nucleus, creating a zygote. This zygote contains a complete set of chromosomes, essential for the development of a new human organism, with half originating from the egg and half from the sperm.