sperm
Sexual reproduction is more complicated. It involves two parents. Special cells called gametes are produced by the parents. A gamete produced by a female parent is generally called an egg . A gamete produced by a male parent is usually called a sperm . An offspring forms when two gametes unite. The union of the two gametes is called fertilization . You can see a human sperm and egg uniting in Figure below . The initial cell that forms when two gametes unite is called a zygote .
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