Why does fertilization restore the full number of chromosomes in a human zygote?

Fertilization restores the full, diploid number of chromosomes in a human zygote because it involves the fusion of two haploid gametes—the sperm and the egg.12

Prior to fertilization, these gametes are produced through a specialized type of cell division called meiosis, which reduces the chromosome count by half, resulting in cells that contain only a single set of chromosomes. During the process of fertilization, the male and female pronuclei meet and combine their genetic material. By uniting these two haploid sets, the zygote reestablishes the characteristic diploid number (two complete sets of chromosomes), which provides the necessary genetic foundation for the development of a new, unique individual.345