Definitions for: Pronucleus

[n] the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote

Webster (1913) Definition: Pro*nu"cle*us, n.; pl. Pronuclei (-[imac]). [NL.
See Pro-, and Nucleus.] (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.

Note: 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 spermatozo["o]n 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.

See Also: cell nucleus, karyon, nucleus

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