a) When do mitosis and meiosis occur? Does meiosis occur when the sperm fuses with the egg? b) Explain what is spermatogenesis and oogenesis.

a) Mitosis occurs throughout the life of an organism for growth, repair, and asexual reproduction. Meiosis occurs only during the formation of gametes (sperm and eggs). Meiosis does not occur when sperm fuses with the egg; this fusion is called fertilization.
b) Spermatogenesis is the process of sperm cell development in the testes, resulting in four haploid sperm cells from one diploid cell. Oogenesis is the process of egg cell development in the ovaries, producing one mature haploid egg cell and three polar bodies from one diploid cell.