ovum, gen. ovi, pl. ova (o´vum, -vI, -va)

The female sex cell. When fertilized by a spermatozoon, an o. is capable of developing into a new individual of the same species; during maturation, the o., like the spermatozoon, undergoes a halving of its chromosomal complement so that, at its union with the male gamete, the species number of chromosomes (46 in humans) is maintained; yolk contained in the ova of different species varies greatly in amount and distribution, which influences the pattern of the cleavage divisions. [L. egg]
alecithal o. an o. in which the yolk is nearly absent, consisting of only a few particles.
blighted o. a fertilized o. whose development has ceased at an early stage.
centrolecithal o. one in which the yolk is mostly located near the center of the egg, as in arthropods.
fertilized o. an o. impregnated by a spermatozoon.
isolecithal o. an o. in which the yolk is evenly distributed throughout the cytoplasm.
Peters' o. an o. with a presumptive fertilization age of about 13 days; for many years, it was one of very few young human embryos recovered in good condition and its study furnished many facts regarding early embryonic changes.
telolecithal o. an o. in which there is a large amount of yolk massed at the vegetative pole, as in the eggs of birds and reptiles.


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