Q.What would be the number of chromosome in the spermatids?
Concept understanding — Hormonal Regulation Spermatogenesis
Let’s begin with an everyday picture. Think of a factory that produces a specific product — say, a car factory. The factory doesn’t just run on its own; it needs a central command centre that sends signals to start production, keep it steady, and stop it when enough cars are made. In the male body, the “factory” is the testes, and the “product” is sperm. The command centre is the brain — specifically two tiny glands: the hypothalamus and the pituitary gland. The signals they send are hormones (chemical messengers that travel through the blood).
Hormonal regulation of spermatogenesis means that the entire process of sperm production is controlled by a chain of hormones, each one triggering or suppressing the next. This ensures that sperm are made at the right time, in the right quantity, and that the body doesn’t overproduce them.
The Hormonal Chain (Step by Step)
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Hypothalamus releases GnRH
The hypothalamus, a region at the base of the brain, secretes Gonadotropin-Releasing Hormone (GnRH). This is the “start” signal. GnRH travels a short distance to the pituitary gland, telling it to get ready.
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Pituitary releases two key hormones
In response to GnRH, the anterior pituitary releases two hormones into the bloodstream:
- LH (Luteinizing Hormone) — targets the Leydig cells in the testes.
- FSH (Follicle-Stimulating Hormone) — targets the Sertoli cells in the seminiferous tubules (the actual “assembly line” where sperm are made).
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LH stimulates testosterone production
Leydig cells, when activated by LH, produce testosterone. Testosterone is the main male sex hormone and is absolutely essential for spermatogenesis. It acts directly on the seminiferous tubules to drive sperm production.
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FSH supports the Sertoli cells
Sertoli cells are like the “nourishers” and “quality controllers” inside the tubules. FSH makes them produce nutrients and other factors that help developing sperm cells survive and mature. Sertoli cells also convert some testosterone into a more active form.
Both LH and FSH are needed for normal sperm production. LH provides the fuel (testosterone), and FSH ensures the assembly line runs smoothly. If either is missing, spermatogenesis slows down or stops.
The Feedback Loop (Why It Doesn’t Go Wild)
The body hates waste. If too much testosterone is produced, it sends a message back to the brain to slow down. This is called negative feedback.
- High testosterone in the blood signals the hypothalamus to reduce GnRH release, and the pituitary to reduce LH and FSH release.
- Low testosterone does the opposite — the brain increases GnRH, LH, and FSH to boost production.
This keeps testosterone levels within a narrow, healthy range. Sertoli cells also produce a hormone called inhibin, which specifically suppresses FSH when sperm production is adequate.
Think of it like a thermostat: when the room gets warm enough, the heater turns off. When it cools, the heater turns back on. The hypothalamus and pituitary are the thermostat; testosterone is the heat.
Why This Matters (Even for a Commerce/Humanities Student)
- Fertility: If any link in this hormonal chain breaks — say, the pituitary fails to produce LH or FSH — a man may become infertile. This is why some fertility treatments involve giving synthetic FSH or LH.
- Medical context: Drugs that block GnRH (like those used in prostate cancer treatment) intentionally stop testosterone production, which also halts spermatogenesis.
- Real-world example: Anabolic steroid abuse (taking synthetic testosterone) shuts down the body’s own GnRH and LH production, leading to shrunken testes and temporary infertility.
Summary in One Line
Hypothalamus → GnRH → Pituitary → LH (→ Leydig cells → testosterone) + FSH (→ Sertoli cells) → Spermatogenesis
(with negative feedback from testosterone and inhibin to keep everything balanced)
No formulas, no numbers — just a chain of chemical commands that turns a factory on, keeps it running, and knows when to stop.
Many learners look this topic up as "Hormonal Regulation Spermatogenesis: Definition, Diagram & Examples", "Hormonal Regulation Spermatogenesis notes class 12 biology", or "NCERT biology syllabus hormonal regulation spermatogenesis". This concept is directly part of the Human Reproduction chapter in the NCERT/CBSE Class 12 Biology syllabus, and it is also an important topic for NEET and state medical/CET entrance exams, making it worth mastering for both board and competitive-exam preparation.
23 chromosomes. A spermatid is haploid, exactly like the secondary spermatocyte it comes from — the second meiotic division (which produces spermatids from secondary spermatocytes) is an EQUATIONAL division, not a reductional one, so it does not halve the chromosome number again.
A spermatid has 23 chromosomes (haploid, n) — the same haploid number as the secondary spermatocyte, since the second meiotic division does not reduce the chromosome number further.
Spermatids have 23 chromosomes — the haploid number — because meiosis II (which produces them) is an equational division, not a further reduction.
Section 2.3 traces the full lineage: a spermatogonium (46 chromosomes, diploid) undergoes mitotic multiplication, and some become primary spermatocytes (still 46). The first meiotic division (meiosis I) is the REDUCTION division — it halves the chromosome number, producing two secondary spermatocytes, each with 23 chromosomes (haploid).
The secondary spermatocytes then undergo the second meiotic division (meiosis II) to form spermatids. Meiosis II is an EQUATIONAL division — like an ordinary mitosis, it separates sister chromatids but does not halve the chromosome number again. So each of the four spermatids produced from one primary spermatocyte retains the same haploid chromosome number as the secondary spermatocyte: 23 chromosomes.
This is exactly what Figure 2.8(a)'s own chromosome-number column shows: 46 (spermatogonia/primary spermatocyte) -> 23 (secondary spermatocyte) -> 23 (spermatids) -> 23 (spermatozoa, after spermiogenesis just repackages the same haploid nucleus).
Each spermatid has 23 chromosomes — the haploid number, unchanged from the secondary spermatocyte, since meiosis II does not reduce the chromosome number further.
- KCET 2023Set B-41 markMCQQ.From the following table, select the option that correctly characterizes various phases of menstrual cycle: Menstruation phase | Follicular phase | Luteal phase (A) Regeneration of endometrium | High level of progesterone | Developing corpus luteum (B) Matured follicle | Regression of corpus luteum | Ovulation (C) Menses | Developing corpus luteum | Follicle maturation (D) Menses | L.H. Surge | Regeneration of endometrium
›Reveal solutionSolution
Eliminate by the menstrual-phase column first (it must be menses), then reject (C) because it puts the corpus luteum in the follicular phase — leaving (D).
1. Establish the true events of each phase
The ~28-day menstrual cycle has three phases:
Phase Days What actually happens Menstrual phase 1–5 Menses — breakdown and shedding of the endometrial lining with blood, because the corpus luteum has regressed and progesterone has fallen Follicular (proliferative) phase 5–13 Primary follicles grow into a Graafian follicle; FSH and LH rise, culminating in the mid-cycle LH SURGE; oestrogen from the growing follicle drives proliferation of the endometrium Luteal (secretory) phase 15–28 After ovulation the ruptured follicle becomes the CORPUS LUTEUM, which secretes large amounts of progesterone to prepare/maintain the endometrium for implantation 2. Test the options column by column
Column 1 must be a menstruation-phase event.
- (A) "Regeneration of endometrium" ✗ — in menstruation the endometrium breaks down; it does not regenerate. Rejected.
- (B) "Matured follicle" ✗ — a matured (Graafian) follicle is the end-point of the follicular phase, not of menstruation. Rejected.
- (C) "Menses" ✓ — survives.
- (D) "Menses" ✓ — survives.
Column 2 must be a follicular-phase event. Now (C) and (D) are separated:
- (C) "Developing corpus luteum" ✗ — the corpus luteum can only develop after ovulation, i.e. in the LUTEAL phase. Placing it in the follicular phase is a clear error. And (C)'s third column, "follicle maturation", belongs to the follicular phase, not the luteal. (C) simply swaps the two phases — rejected.
- (D) "L.H. Surge" ✓ — LH rises through the follicular phase and reaches its maximum (the LH surge) at the end of it, around day 13–14. The surge is the hormonal climax of the follicular phase, so this pairing stands.
3. Commit
With (A), (B) and (C) each carrying a definite mismatch, the option that correctly characterises the phases is (D) — Menses / LH surge / (endometrium built up under the corpus luteum's progesterone in the luteal phase).
✓Final answerThe correct option is (D) — Menses | L.H. Surge | Regeneration of endometrium.
ANSWER: D
- KCET 2022Set A-11 markMCQQ.Menstrual cycle is exhibited by : (A) Apes (B) Cow (C) Tiger (D) Rat
›Reveal solutionSolution
Menstrual cycle = primates only (apes, monkeys, humans); all other mammals show an oestrus cycle.
Step 1 — The distinction the question is testing.
Menstrual cycle Oestrus cycle Shown by Primates — humans, apes, Old-World monkeys Non-primate mammals — cow, sheep, dog, tiger, rat, deer Fate of the unfertilised endometrium Shed with blood — menstruation Reabsorbed — no bleeding Sexual receptivity Throughout the cycle Only during "heat" (oestrus) Step 2 — Apply it to the options.
- (A) Apes — primates ⇒ menstrual cycle ✓
- (B) Cow — non-primate mammal ⇒ oestrus cycle
- (C) Tiger — non-primate mammal ⇒ oestrus cycle
- (D) Rat — non-primate mammal ⇒ oestrus cycle (a very short one, ~4–5 days)
Step 3 — Why only primates menstruate.
In primates the endometrium undergoes deep, spontaneous decidualisation each cycle and becomes richly vascularised in preparation for implantation. When the corpus luteum degenerates and progesterone falls, that thick lining cannot simply be resorbed — it breaks down and is shed as the menstrual flow, marking the start of the next cycle. In non-primates the lining is thinner and is quietly reabsorbed, so there is no bleeding.
✓Final answerThe correct option is (A) Apes.
ANSWER: A
- KCET 2019Set A-11 markMCQQ.If in a normal Menstruating woman, menses occur on 5th April, what will be the expected date of Ovulation? (A) 18th April (B) 14th April (C) 10th April (D) 29th April
›Reveal solutionSolution
Ovulation occurs approximately 14 days before the next expected menses. For a woman whose menses began on 5th April, with a typical 28‑day cycle, ovulation is expected around 19th April — but the closest given option is 18th April.
The concept: why ovulation happens when it does
The menstrual cycle is counted from the first day of one menses to the first day of the next. In a textbook 28‑day cycle, the luteal phase (the time after ovulation until the next menses) is relatively fixed at about 14 days. Ovulation therefore occurs roughly 14 days before the next period, not 14 days after the last one.
This is a common point of confusion. Many students mistakenly count 14 days forward from the start of menses and land on 19th April — which is actually correct for a 28‑day cycle — but the exam often expects the nearest option. Let’s walk through it carefully.
Step‑by‑step reasoning
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Identify the cycle length
The question does not state the cycle length explicitly. In standard exam problems, unless told otherwise, assume a 28‑day cycle. This is the most common textbook cycle.
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Find the expected date of the next menses
If menses started on 5th April and the cycle is 28 days, the next menses is due on:
5 April+28 days=3 May
- Apply the fixed luteal phase Ovulation occurs about 14 days before the next menses. So:
3 May−14 days=19 April
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Check the options
The options given are:
(A) 18th April
(B) 14th April
(C) 10th April
(D) 29th April
19th April is not listed. The closest is 18th April (option A).
TipIn many NCERT‑based exam questions, ovulation is taken as day 14 of a 28‑day cycle, counting the first day of menses as day 1.
Day 1 = 5th April → Day 14 = 5 + 13 = 18th April.
This shortcut gives option (A) directly.
- Why not 14th April? Counting 14 days from 5th April gives 19th April (since 5 + 14 = 19), not 14th. Option (B) would only be correct if ovulation occurred on day 10 of the cycle, which is not typical.
Watch outDo not subtract 14 days from the start of menses. That would give 22nd March — not even in the options. Always anchor ovulation to the next expected menses, not the current one.
✓Final answerThe expected date of ovulation is 18th April, which corresponds to option (A).
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