Gametogenesis: Spermatogenesis and Oogenesis
Gametogenesis is the formation of haploid gametes from diploid germ cells through mitotic multiplication, growth and meiotic divisions; in males it is spermatogenesis and in females it is oogenesis.
In one line: Sperm formation is continuous and four-fold; ovum formation is cyclic, paused and one-functional.
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- Spermatogenesis occurs in seminiferous tubules after puberty and produces many functional sperm continuously.
- Spermatogonia divide, grow into primary spermatocytes, undergo meiosis I to form secondary spermatocytes and meiosis II to form spermatids, which transform into spermatozoa by spermiogenesis.
- Oogenesis begins before birth.
- Oogonia form primary oocytes that remain arrested until puberty.
- Usually one secondary oocyte is released during ovulation, and meiosis II completes only after sperm entry.
- Hormones regulate both processes: FSH supports gamete development, LH stimulates Leydig cells in males and ovulation-related events in females.
Example
Rule to remember
Meiotic rule: diploid germ cell undergoes meiosis to form haploid gametes.
Spermatogenesis gives four functional haploid sperm; oogenesis usually gives one functional ovum and polar bodies.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
If asked to name products of meiosis I in spermatogenesis, answer: a primary spermatocyte undergoes meiosis I to form two haploid secondary spermatocytes.
Method you can reuse
- 1For spermatogenesis: spermatogonia multiply; primary spermatocytes form; meiosis I produces secondary spermatocytes; meiosis II produces spermatids; spermiogenesis forms spermatozoa.
- 2For oogenesis: oogonia form primary oocytes before birth; primary oocytes remain arrested; after puberty one resumes meiosis; secondary oocyte is ovulated; meiosis II completes after sperm entry.
Visual tip
Useful labels include spermatogonium, primary spermatocyte, secondary spermatocyte, spermatid, spermatozoon, oogonium, primary oocyte, secondary oocyte, ovum and polar bodies. Notice equal versus unequal division.
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
Why does oogenesis usually produce one functional ovum while spermatogenesis produces four functional sperm from one primary cell?
Think first, then show answerHide answer
Common wrong answer
A common wrong answer is saying that the secondary oocyte is a completed ovum at ovulation. It is not a completed ovum until meiosis II is completed after sperm entry.
Don't mix this up
Exam tip
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
Answer plan
- 1
Enough for 1 mark
Gametogenesis is the formation of haploid gametes from diploid germ cells through mitotic multiplication, growth and meiotic divisions; in males it is spermatogenesis and in females it is oogenesis.
- 2
Add for 2 marks
Spermatogenesis occurs in seminiferous tubules after puberty and produces many functional sperm continuously.
- 3
Add for 3 marks
Spermatogonia divide, grow into primary spermatocytes, undergo meiosis I to form secondary spermatocytes and meiosis II to form spermatids, which transform into spermatozoa by spermiogenesis.
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