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fertilization fer·til·i·za·tion (fûr'tl-ĭ-zā'shən)
The union of male and female gametes to form a zygote, a process that begins with the penetration of the secondary oocyte by the spermatozoon and is completed with the fusion of the male and female pronuclei.
The joining of sex cells to form a new living thing. In humans, a male sperm joins a female ovum, or egg; the resulting zygote divides into a multicelled structure that implants in the womb and grows into an embryo. In plants, pollen grains, containing the male sex cells, enter the female sex cells in the pistil; from this union, fruit eventually grows. When fertilization occurs within a single flower, we call it self-fertilization. (See cross-fertilization.)