pronucleus

pronucleus A cell nucleus with a haploid (halved) set of chromosomes—23 chromosomes in humans—that results from division (meiosis) of a germ cell. 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.