Definition of Pronucleus

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Pronucleus: A cell nucleus with a haploid set of chromosomes (23 chromosomes in humans) resulting from meiosis (germ-cell division). The male pronucleus is the sperm nucleus after it has entered the ovum at fertilization but before fusion with the female pronucleus. Similarly, the female pronucleus is the nucleus of the ovum before fusion with the male pronucleus.