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Fer­til­i­sa­tion or fer­til­iza­tion (also known as con­cep­tion, fecun­da­tion and syn­gamy) is the fusion of gametes to ini­ti­ate the devel­op­ment of a new indi­vid­ual organ­ism. In ani­mals, the process involves the fusion of an ovum with a sperm, which even­tu­al­ly leads to the devel­op­ment of an embryo. Depend­ing on the ani­mal species, the process can occur with­in the body of the female in inter­nal fer­til­i­sa­tion, or out­side (exter­nal fer­til­i­sa­tion). The cycle of fer­til­i­sa­tion and devel­op­ment of new indi­vid­u­als is called sex­u­al reproduction.