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The pronucleus is the nucleus of either the sperm or the egg that develops after fertilization. Following fertilization and completion of meiosis II, the egg’s DNA will decondense, and the female pronucleus will form. Similarly, the sperm DNA will also decondense and the male pronucleus will form. In many species, the male pronucleus is larger than the female one. A diploid zygote will be produced when the haploid male and female pronuclei fuse just prior to the first mitotic division.