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Each egg is fertilized independently, and each becomes an embryo. With identical twins, one egg is fertilized by one sperm, and the embryo splits at some later stage to become two. Double fertilization gives rise to an endosperm that provides nourishment to the developing embryo. It increases the viability of the seeds of angiosperms. It utilizes both the male gametes produced by the pollen grains. Occasionally, two sperm are known to fertilize a single egg; this 'double fertilization' is thought to happen in about 1% of human conceptions.

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