OOGENESIS

What is gametogenesis and where does it occur?

Development of male and female germ cells; occurs only in testes (male) and ovaries (female).

Where does oogenesis occur?

In the cortical tissue of the ovary.

What is an ovogonium and when is it present?

A diploid stem cell (2n) found only in fetal ovaries.

What happens to the majority of the 7 million primordial follicles?

Most undergo degeneration (atresia).

What does each primordial follicle contain at birth?

A primary oocyte (2n) arrested in prophase I (diplotene) of meiosis I.

When are ovaries inactive and when do they reactivate?

Inactive from fetal development until puberty, when ovulation begins.

What happens to the primary oocyte during ovulation?

Completes meiosis I → becomes secondary oocyte (n) and first polar body.

When does meiosis II complete in oogenesis?

Only if fertilization occurs; oocyte is arrested in metaphase II until then.

What happens to unfertilized oocytes?

They are lost via menstruation.

How many oocytes are shed in a woman’s lifetime?

Approximately 360–480 eggs over 30–40 years of menstruation.

What happens to ovulation during pregnancy?

It is hormonally suppressed.

What is gametogenesis and where does it occur?

Development of male and female germ cells; occurs only in testes (male) and ovaries (female).

What is the ploidy and status of the oogonium?

Diploid (2n); a mitotically active stem cell present only during fetal development.

What is the fate of most oogonia?

They enter meiosis I, become primary oocytes, and are arrested in prophase I (diplotene).

What is diplotene arrest and when does it begin?

A subphase of prophase I where primary oocytes are paused starting from fetal life until puberty.

What hormonal event triggers ovulation and meiosis I resumption?

A surge in luteinizing hormone (LH) at puberty triggers completion of meiosis I in one follicle per cycle.

What is formed after meiosis I completes in the oocyte?

A secondary oocyte (n) and a first polar body, which degenerates.

What is the ploidy and meiotic status of the ovulated oocyte?

Haploid (n); arrested in metaphase II, waiting for fertilization.

When does meiosis II complete in oogenesis?

Only upon sperm fertilization, leading to formation of a mature ovum and second polar body.

What type of follicle surrounds the primary oocyte at birth?

Primordial follicle, which can mature later into a primary and then pre-ovulatory (Graafian) follicle.