pronucleus

biology

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 13, 2026

Quick Summary

A pronucleus is the nucleus of a male or female gamete (egg or sperm) before it fuses with the nucleus of another gamete during fertilization. In human development, after a sperm penetrates an egg, its nucleus swells and becomes the male pronucleus. The egg's nucleus, after completing its final maturation division, becomes the female pronucleus. These two pronuclei then merge, combining their chromosomes to form a zygote, which is the first cell of a new individual. The term "pronuclear" relates to or resembles a pronucleus.1234

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

4 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

fertilization
Formation of the zygote nucleus
…nucleus, now called the male pronucleus, begins to swell, and its chromosomal material disperses and becomes similar in appearance to that of the female pronucleus. Although the membranous envelope surrounding the male pronucleus rapidly disintegrates in the egg, a new envelope promptly forms around it. The male pronucleus, which rotates…
Read More
…nucleus, now called the male pronucleus, begins to swell, and its chromosomal material disperses and becomes similar in appearance to that of the female pronucleus. Although the membranous envelope surrounding the male pronucleus rapidly disintegrates in the egg, a new envelope promptly forms around it. The male pronucleus, which rotates…
Read More

protist
Reproduction and life cycles
…produce a number of haploid pronuclei; all but one of these pronuclei in each organism will disintegrate. The remaining pronuclei divide mitotically; one pronucleus from each organism is exchanged, and the new micronuclei and macronuclei of the next generation are formed. Following the exchange of the pronuclei and the subsequent…
Read More
…produce a number of haploid pronuclei; all but one of these pronuclei in each organism will disintegrate. The remaining pronuclei divide mitotically; one pronucleus from each organism is exchanged, and the new micronuclei and macronuclei of the next generation are formed. Following the exchange of the pronuclei and the subsequent…
Read More

prenatal development
Fertilization
…nucleus, now called the male pronucleus, and the tail detaches. It is during the progress of these events that the oocyte initiates its final maturation division. Following the separation of the second polar body (one or two polar bodies are produced during division), the oocyte nucleus typically reconstitutes and is…
Read More
…nucleus, now called the male pronucleus, and the tail detaches. It is during the progress of these events that the oocyte initiates its final maturation division. Following the separation of the second polar body (one or two polar bodies are produced during division), the oocyte nucleus typically reconstitutes and is…
Read More