To reproduce sexually, an organism must create haploid cells, or gametes, from diploid cells in animals, fuse with the mother's haploid cells, called eggs. Cell fusion produces a diploid cell called a zygote, which undergoes many rounds of cell division to create the entire body of the new individual. The cells produced from the initial fusion event include somatic cells that form most of the tissues of the body as well as the germ-line cells that give rise to the next generation of progeny. Allele, bivalent, germ, pedigree, pollen, meiosis, gametes, somatic, eggs, zygote, mitosis, sperm.