Gametogenesis- Oogenesis
OOGENESIS
- Oogenesis refers to the process of formation of ova from the primitive germ cells.
- Unlike fetal testis (in which spermatogenesis begins at puberty) the fetal ovary begins oogenesis by 10 weeks of gestation.
- The sequence of events in oogenesis are:-
1) The primitive germ cells undeergo mitotic divisions to form oogonia (diploid cells). Oogonium is unique in that it is the only female cell in which both ‘X’ chromosomes are active.
2) The oogonia proliferate by mitosis to form primary oocytes (diploid cells). Oogonium is unique in that it is the only fema;le cell in which both ‘x’ chromosomeas are active.
3) Primary oocytes formed from the oogonia enter a prolonged prophase (diplotene stage) of the first meiotic divisionn and remain in this stage until ovulation occurs after puberty.
4) Primary oocytes completes the first meiotic division at puberty just before ovulation to form secondary oocyte (haploid cell) and 1st polor body.
5) Secondary oocyte immediately begins second meiotic division but this division stops at metaphase and is completed only if the mature ovum (ootid) is fertilised with sperm. At that time second polor body (polocyte) is extruded and the fertilised ovum proceeds to form a new individual. Fertilisation normally occurs in the ampulla of fallopian tube.
Exam Question
- Primary oocyte is Maximum in number in 5 month fetus
- Primary oocyte ls in prophase arrest
- At birth, oocytes are in Resting phase between prophase and metaphase of 1st meiotic division of developÂment
- Primary Oocyte remains in ovary in Prophase
- Primary oocyte is arrested at prophase till puberty
- Primary oocyte is hormonally induced to resume the first meiotic division during onset of puberty
- Secondary oocyte enters the second meiotic division just before ovulation and arrests at metaphase
- Polar bodies are formed during Oogenesis
- Ovary Develops in genital ridge
- Sex cords are derived from coelomic epithelium
- At birth ovary contains 2 million folliclesCells which surround the oocyst in graafian follicle are called Cumulus oophoricus
- After first meiotic division, the primary oocyte remains arrested in Diplotene stage
- In oogenesis, first meiotic division completes Before ovulation
- One primary oocyte forms 1ovum