Oogenesis

Definition

The process by which a diploid germ cell undergoes meiosis and differentiation to produce a mature, haploid ovum competent for fertilization. In insects and other arthropods, oogenesis occurs within ovarioles of the ovary, progressing through stages from oogonium to primary oocyte, secondary oocyte, and finally the ovum, often accompanied by nutritive contributions from nurse cells and follicular epithelium.

Etymology

Greek ōon (egg) + genesis (origin, creation)

Example

In Drosophila melanogaster, oogenesis proceeds through 14 morphologically distinct stages within each ovariole; nurse cells polyploidize and transport RNAs and proteins into the growing oocyte through cytoplasmic bridges, while the follicle cells surrounding the egg chamber pattern the future eggshell.

Synonyms

• ovogenesis

Related Terms

• Spermatogenesis
• Ovariole
• nurse cell
• follicle cell
• Vitellogenesis
• oocyte
• germarium
• meristic ovary
• panoistic ovary

Usage Notes

Contrasts with spermatogenesis, the male equivalent. In arthropods, oogenesis is often classified by ovary type: panoistic ovaries lack nurse cells (common in basal insects and many non-insect arthropods), while meroistic ovaries contain nurse cells that support oocyte development (characteristic of most higher insects). The term properly refers to the entire developmental sequence, not merely the final maturation events.