ovum: Oogenesis

Ova are produced in the ovary of the female; they are formed from reproductive cells (called primordial germ cells) in a process called oogenesis. In this maturation process a germ cell builds up its food supply and then undergoes a series of cell divisions (called meiosis), by which the number of chromosomes in the mature ovum is reduced by half. In oogenesis in animals only one of the four cells formed by meiotic division is functional. In this ovum all the yolk from the original cell is collected; the three other, yolkless, cells are called polar bodies and never develop further. Maturation also occurs in the formation of sperm (spermatogenesis), but in spermatogenesis, in contrast to oogenesis, all four of the cells formed by meiotic division are functional.

Sections in this article:

• Introduction
• Plant Ova
• Fertilization and Maturation
• Oogenesis

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