Oogenesis: female gametogenesis


Gametogenesis is the process of formation of the male and female gamete, i.e. of the cell with haploid chromosomal kit which, joining a pair (gamia) in the act of fertilization, gives rise to a new individual.


In women, this cell is the egg, which is why gametogenesis is called oogenesis.

The development of the egg begins even before the birth of the woman who carries it: from 8 to 20 weeks after the fetus has begun to grow, the cells that are about to become mature ova have multiplied and, by the time the woman herself is born, all the egg cells that the ovaries will release during the female’s active reproductive years are already present in the ovaries. These cells, known as primary ova, number about 400,000. The primary ova remain dormant until just before you ovulate (the stage in the menstrual cycle when an egg is released from the ovaries). Some eggs may not mature for 40 years; others degenerate and never mature.

The egg cell remains as the primary ovum until its release from the ovary. The egg then undergoes cell division: the nucleus divides so that half of its chromosomes go into one cell and half into another. One of these two new cells is usually larger than the other and is known as a secondary egg; the smallest cell is known as a polar body. The secondary egg grows in the ovary until it reaches maturity; then it detaches and is carried into the fallopian tubes. Once in the fallopian tube, the secondary egg is suitable for fertilization by male sperm.

Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.

She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform, Maternicity.com.

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