American Heritage® Dictionary of the English Language, Fourth Edition
- n. The haploid nucleus of a sperm or egg before fusion of the nuclei in fertilization.
Century Dictionary and Cyclopedia
- n. A primitive nucleus; the nucleus of an ovum or of a spermatozoön before these have united to form the definitive nucleus of an impregnated ovum. That of the ovum is the female, that of the spermatozoön the male pronucleus. The formation of the female pronucleus commonly occurs in a ripe ovum after the extrusion of the particles of yolk known as the polar globules of Robin, and it is that part of the original germinal vesicle which remains behind after such extrusion, receding from the surface of the ovum and assuming a spherical form. The male pronucleus is simply the head of a spermatozoön buried in the yolk, and about to blend its substance with that of the female pronucleus. See feminonucleus, masculonucleus.
- n. In botany, the nucleus of a conjugating gamete, which on coalescing with another pronucleus forms the germ-nucleus.
GNU Webster's 1913
- n. (Biol.) One of the two bodies or nuclei (called
maleand female pronuclei) which unite to form the first segmentation nucleus of an impregnated ovum.
- n. the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote
“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.”
“Close to it lies its centrosomes (Fig. 35, _ce_), and there is thus formed what is known as the _male pronucleus_ (Fig. 35-40, _mn_).”
“The chromatin material, in both the male and female pronucleus, soon breaks up into a network in which it is no longer possible to see that each contains two chromosomes (Fig. 41).”
“-- Completion of the process of extrusion of the chromatic material; _fn_ shows the two chromosomes retained in the egg forming the female pronucleus.”
“The tail by which it has been moving is cast off, and the head containing the chromosomes and the centrosome enters the egg, forming what is called the male pronucleus (Figs. 35-38, _mn_).”
“In this way the centrosome approaches the female pronucleus, and thus finally the two nucleii are brought into close proximity.”
“Now the centrosome, which is beside the male pronucleus, shows signs of activity.”
“The nucleus of the mature ovum is termed the female pronucleus.”
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