pronucleus Meaning, Definition & Usage

noun the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote

NL. See Pro-, and Nucleus.

plural Pronuclei

(Biol.) One of the two bodies or nuclei (called male and female pronuclei) which unite to form the first segmentation nucleus of an impregnated ovum. ✍ In the maturing of the ovum preparatory to impregnation, a part of the germinal vesicle (see Polar body, under Polar) becomes converted into a number of small vesicles, which aggregate themselves into a single clear nucleus. which travels towards the center of the egg and is called the female pronucleus. In impregnation, the spermatozoön which enters the egg soon loses its tail, while the head forms a nucleus, called the male pronucleus, which gradually travels towards the female pronucleus and eventually fuses with it, forming the first segmentation nucleus.