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Pronunciation: pro-nu'kle-us, -kle-i


  1. One of a pair of nuclei undergoing fusion in karyogamy.
  2. In embryology, the nuclear material of the head of the sperm (male pronucleus) or of the oocyte (female pronucleus), after the oocyte has been penetrated by the sperm; each pronucleus normally carries a haploid set of chromosomes, so that the merging of the pronuclei in fertilization reestablishes diploidy.

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© Copyright 2018 Wolters Kluwer. All Rights Reserved. Review date: Sep 19, 2016.