The haploid nucleus of a sperm or egg before fusion of the nuclei in fertilization. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "pronucleus" in a sentence
"In the process a pronucleus is formed which then combines with the female pronucleus."
"If, however, it takes place before, the male pronucleus simply remains dormant in the egg while the polar cells are being protruded, and not until after that process is concluded does it begin again to show signs of activity which result in the cell union."
"It becomes surrounded by prominent rays to form an aster (Fig. 41, _ce_), and then it begins to move toward the female pronucleus, apparently dragging the male pronucleus after it."