oogenesis is the process through which a primordial egg cell (or ovum) develops into a mature ovum in the female reproductive system. The egg’s development begins before the female who carries it is even born; cells that will become mature ova have been multiplying for 8 to 20 weeks after the foetus has begun to grow, and by the time the female is born, all of the egg cells that the ovaries will release during the active reproductive years of the female have already been present in the ovaries.

The main ova, or cells that make up the ova, number roughly 400,000. The primary ova are quiescent until immediately before ovulation, when the ovary releases one egg. Some egg cells take up to 40 years to mature, while others degenerate and never mature.

Until the time comes for the egg cell to be released from the ovary, it remains a primary ovum. The egg then divides into two cells. The nucleus splits into two cells, with half of the chromosomes going to one cell and the other to the other. The secondary ovum is usually larger than the polar body, and one of these two new cells is known as the secondary ovum.

The secondary ovum develops in the ovary until it reaches maturity, at which point it breaks out and enters the fallopian tubes. The secondary egg cell, once in the fallopian tubes, is amenable for fertilisation by male sperm cells.