Final answer:
The process that joins the egg and sperm to restore the original chromosome number of the organism is B. fertilization
Step-by-step explanation:
Fertilization is the process in which gametes (an egg and sperm) fuse to form a zygote, which is the first cell of a new organism. The egg and sperm each contain one set of chromosomes, and through fertilization, they combine to form a diploid zygote with a complete set of chromosomes.
Meiosis (option A) is the process of cell division that produces haploid gametes by reducing the number of chromosomes in half. It is necessary for sexual reproduction, but it does not restore the original chromosome number of the organism.Mitosis (option C) is another type of cell division that occurs in somatic cells and results in two identical daughter cells. It does not involve the fusion of gametes or restoration of chromosome number.
Replication (option D) is the process of DNA duplication that occurs before cell division. It is necessary for both meiosis and mitosis, but not specifically for joining the egg and sperm. Therefore the correct answer is B. fertilization