In order to fertilize an egg, sperm must first be readed by capacitation. Secretions in the uterus render the sperm hyperactive (whipping tail and moving head) and the acrosome in the sperm head is made able to penetrate and fertilize the ovum.
Meiosis is completed in the oocyte after fusion of the sperm with the egg, as its nucleus enters the oocyte. During fertilization, the haploid nuclei of egg and sperm combine to form a diploid zygote. The oocyte can be fertilized 12-24 hrs after ovulation (sperm live 5-6 days).
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