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Human reproduction carries many small, exact facts: chromosome numbers at each stage, which hormone acts on which cell, which day ovulation happens. NEET questions often test the differences between spermatogenesis and oogenesis, or ask you to count cells. This post sets the two processes side by side, works through the counting, and puts the menstrual cycle hormones in order, all from the NCERT chapter.
What does the syllabus include?
The NEET (UG) 2026 syllabus lists male and female reproductive systems, microscopic anatomy of testis and ovary, "gametogenesis-spermatogenesis & oogenesis", the menstrual cycle, fertilisation, embryo development up to blastocyst formation, implantation, and elementary ideas of pregnancy, placenta formation, parturition and lactation. All of these are in NCERT's Class 12 chapter on human reproduction. Check the syllabus for your exam year when it is notified.
How does spermatogenesis work?
NCERT describes the sequence in the seminiferous tubules:
Spermatogonia (diploid, 46 chromosomes) multiply by mitosis.
Some become primary spermatocytes, which undergo meiosis I to give two secondary spermatocytes, each with 23 chromosomes.
Meiosis II gives four haploid spermatids.
Spermatids change into sperms by spermiogenesis, and sperms are released from the tubules by spermiation.
Spermatogenesis begins at puberty, when GnRH from the hypothalamus rises. GnRH makes the anterior pituitary release LH, which acts on Leydig cells to make androgens, and FSH, which acts on Sertoli cells, which secrete factors that help spermiogenesis.
How is oogenesis different?
It begins before birth. NCERT says a couple of million oogonia form in each fetal ovary, and no more are added after birth.
They enter meiosis I and stay arrested in prophase I as primary oocytes. Many follicles degenerate, so only 60,000 to 80,000 primary follicles are left in each ovary at puberty.
In the tertiary follicle, the primary oocyte completes meiosis I. This division is unequal: one large haploid secondary oocyte and a tiny first polar body.
The Graafian follicle releases the secondary oocyte at ovulation.
Meiosis II is completed only when a sperm enters. It is also unequal, giving the ovum and a second polar body.
Worked example: counting cells and chromosomes
How many sperms come from 100 primary spermatocytes, and how many ova from 100 primary oocytes?
Each primary spermatocyte → 2 secondary spermatocytes → 4 spermatids → 4 sperms. So 100 primary spermatocytes give 100 × 4 = 400 sperms.
Each primary oocyte gives only one ovum, because both divisions put almost all the cytoplasm into one cell. So 100 primary oocytes give 100 ova.
Turned around: 100 sperms need 100 ÷ 4 = 25 primary spermatocytes, but 100 ova need 100 primary oocytes.
Chromosome numbers in humans: spermatogonium 46, primary spermatocyte 46, secondary spermatocyte 23, spermatid 23, sperm 23, first polar body 23, ovum 23, zygote 23 + 23 = 46.
What controls the menstrual cycle?
NCERT gives the average cycle as about 28/29 days. In order:
Menstrual phase (3 to 5 days): the endometrium breaks down because the ovum was not fertilised.
Follicular phase: LH and FSH rise gradually. Follicles grow into a Graafian follicle and secrete estrogens, and the endometrium regenerates.
Ovulation (about day 14): LH and FSH both peak mid-cycle. The rapid rise in LH, the LH surge, makes the Graafian follicle rupture and release the ovum.
Luteal phase: the remaining follicle becomes the corpus luteum, which secretes large amounts of progesterone to maintain the endometrium for implantation. If there is no fertilisation, the corpus luteum degenerates, the endometrium breaks down and a new cycle starts.
NCERT notes that cycles stop around 50 years of age (menopause), and that during pregnancy all events of the cycle stop.
What happens after fertilisation?
Fertilisation takes place in the ampullary region of the fallopian tube. Cleavage gives 2, 4, 8 and 16 cells (blastomeres); the 8 to 16 cell stage is the morula, which becomes the blastocyst, with an outer trophoblast and an inner cell mass. The trophoblast attaches to the endometrium (implantation), and the inner cell mass becomes the embryo. The placenta produces hCG, hPL, estrogens and progestogens; NCERT notes that hCG, hPL and relaxin (from the ovary, late in pregnancy) are produced only during pregnancy.
Which mistakes cost the most marks?
Swapping Leydig and Sertoli cells. LH acts on Leydig cells; FSH acts on Sertoli cells.
Saying meiosis II finishes before ovulation. It finishes only after sperm entry.
Counting 4 ova per primary oocyte. It is one.
Crediting the corpus luteum mainly with estrogen. NCERT stresses large amounts of progesterone.
Putting fertilisation in the uterus. It is in the ampullary region of the fallopian tube.
A practice routine
Two research findings shape this routine. In Roediger and Karpicke (2006), students who practised recalling a passage remembered more after two days and a week than students who restudied it, even though restudying made them more confident. In seven experiments, Wammes, Meade and Fernandes (2016) found that drawing words led to better free recall than writing them out. Those studies used word lists and prose, but the habit transfers well to labelled diagrams.
Draw from memory (twice a week): spermatogenesis and oogenesis side by side, with chromosome numbers at each stage. Then check against Figure 2.8 in NCERT.
Hormone timeline: draw a 28-day line and mark when LH, FSH, estrogen and progesterone rise and fall.
Counting drill: five questions like the worked example, in both directions.
Space your returns with our spaced revision schedule, and see why NCERT matters for NEET for reading the chapter actively. Meiosis itself is covered in our guide to the cell cycle.
If a step such as the arrest in prophase I does not make sense, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, each with its own lesson, so you can go back to the underlying idea.
Today, draw both gametogenesis pathways from memory with chromosome numbers, then correct them against NCERT.
