OOGENESIS – FEMALE REPRODUCTIVE SYSTEM Notes and MCQ for NEET, GPAT, BSc, Nursing Exams
Definition:
Oogenesis is the process by which ova (female gametes) are produced from primordial germ cells in the ovaries.
It begins before birth, pauses, and completes after puberty during ovulation and fertilization.
STEPS OF OOGENESIS (CHART FORMAT)
| Stage | Cell Type | Chromosome (n) | DNA Content | Event |
|---|---|---|---|---|
| 1. Fetal Life | Oogonium | 2n | 2C | Mitosis to form many oogonia |
| Primary Oocyte | 2n | 4C | Begins Meiosis I → arrests in Prophase I (Dictyotene stage) | |
| 2. Puberty Onward | Primary Oocyte | 2n | 4C | Each month, completes Meiosis I just before ovulation |
| Secondary Oocyte | n | 2C | Forms with 1st polar body (small, degenerates) | |
| 3. After Ovulation | Secondary Oocyte | n | 2C | Arrests in Metaphase II |
| Ovum | n | 1C | Meiosis II completes only if fertilization occurs → forms 2nd polar body |
Summary Timeline:
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Before Birth: Oogonia → Primary oocytes (arrested in Prophase I)
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Puberty to Menopause: Monthly cycle activates a few primary oocytes
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Ovulation: Secondary oocyte released (arrested in Metaphase II)
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Fertilization: Meiosis II completes → mature ovum
IMPORTANT POINTS:
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Total number of primary oocytes at birth: ~1–2 million
-
At puberty: ~400,000 remain
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Oocytes ovulated in lifetime: ~400–500
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Only one ovum is usually produced per menstrual cycle
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Polar bodies are by-products of division and do not form ova
MCQs on Oogenesis
1. Oogenesis begins at which stage of life?
A. Puberty
B. Birth
C. Fetal life
D. Menarche
Answer: C. Fetal life
2. The primary oocyte is arrested in which phase of meiosis?
A. Metaphase I
B. Prophase I
C. Anaphase II
D. Metaphase II
Answer: B. Prophase I
3. When does the secondary oocyte complete Meiosis II?
A. At ovulation
B. After fertilization
C. At puberty
D. At menopause
Answer: B. After fertilization
4. How many polar bodies are formed during oogenesis?
A. 1
B. 2
C. 3
D. 4
Answer: C. 3 (one in Meiosis I, two in Meiosis II including possible division of first polar body)
5. What is the chromosomal content of a secondary oocyte?
A. 2n, 4C
B. n, 2C
C. n, 1C
D. 2n, 2C
Answer: B. n, 2C