Final answer:
Fusion of haploid gametes is called fertilization, which leads to the formation of a diploid zygote. The haploid cells are produced by meiosis and they develop into mature gametes through gametogenesis.
Step-by-step explanation:
The fusion of haploid gametes is known as fertilization. Fertilization results in the formation of a diploid zygote, containing genetic information from both parent organisms. The process leading up to the creation of gametes is meiosis, which produces haploid cells from a diploid state. In animals, this includes the development of haploid cells into mature gametes capable of fertilization through a process called gametogenesis.
Essentially, the haploid cells produced at the end of meiosis are not yet full-fledged gametes - they must undergo further development. In males, this development is termed spermatogenesis and results in sperm cells, while in females, it is called oogenesis and leads to the creation of egg cells.