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Fertilization is the union of two gametes, or male and female sex cells, to produce a cell, from which a new individual, animal or plant, develops. The sex cells contain half the normal number of chromosomes, and fertilization therefore produces a cell with the normal number of chromosomes for any particular species. Fertilization may take place outside the organism's body (in-utro fertilization), or inside the female (in-vivo fertilization) as a result of copulation.

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