Explore human reproduction and developmental biology. By the end of this module, you will understand:
Estimated Reading Time: 25 minutes | Difficulty Level: Moderate | Prerequisites: None.
This knowledge forms the foundation of obstetrics, gynecology, fertility management, and public health coordination.
After fertilisation the zygote undergoes cleavage: zygote → morula → blastocyst → implantation in the uterine wall. The blastocyst's trophoblast helps form the placenta, the organ of exchange between mother and foetus. Parturition (childbirth) is triggered by oxytocin; lactation is stimulated by prolactin, with the first milk (colostrum) rich in antibodies.
| Phase | Days | Key events & hormones |
|---|---|---|
| Menstrual | 1–5 | Endometrium sheds (no fertilisation); low ovarian hormones |
| Follicular / proliferative | 6–13 | FSH matures a Graafian follicle; rising oestrogen rebuilds the endometrium |
| Ovulatory | ~14 | LH surge ruptures the follicle → ovulation (release of the secondary oocyte) |
| Luteal / secretory | 15–28 | Corpus luteum secretes progesterone, maintaining the endometrium; if no pregnancy it regresses and the cycle restarts |
The cycle is absent during pregnancy and stops at menopause. It is controlled by the hypothalamus–pituitary–ovary axis (GnRH → FSH/LH → oestrogen/progesterone).
| Category | Examples | NEET High-Yield Mechanism |
|---|---|---|
| Copper IUD | CuT, Cu7, Multiload 375 | Releases \(Cu^{2+}\) suppressing sperm motility |
| Hormonal IUD | Progestasert, LNG-20 | Makes uterus unsuitable for implantation |
| Surgical | Vasectomy, Tubectomy | Blocks gamete transport (sterilization) |
❌ Misconception: Oogenesis produces four functional eggs from one germ cell.
✔ Correction: Oogenesis produces only one functional mature ovum and two or three non-functional polar bodies that degenerate.
1. (NEET PYQ) Which of the following is a copper-releasing IUD?
Correct Answer: C. Multiload 375
Explanation: Multiload 375 is a copper-releasing IUD, whereas Lippes loop is non-medicated, and LNG-20 / Progestasert are hormone-releasing IUDs.
Mendel's laws: the Law of Dominance, the Law of Segregation (alleles separate during gamete formation) and the Law of Independent Assortment (genes on different chromosomes assort independently). A monohybrid cross gives a 3:1 phenotypic (1:2:1 genotypic) ratio; a dihybrid cross gives 9:3:3:1.
| Pattern | Example |
|---|---|
| Incomplete dominance | Pink Mirabilis flowers (RR × rr → Rr pink) |
| Co-dominance | Human AB blood group (both A and B expressed) |
| Multiple alleles | ABO blood groups (IA, IB, i) |
| Sex-linked (X-linked recessive) | Haemophilia, colour blindness |
1. (NEET PYQ) In sickle-cell anemia, the point mutation substitutes glutamic acid with:
Correct Answer: B. Valine
Explanation: Sickle-cell anemia is caused by transversion substituting Glutamic acid with Valine at the 6th position of the \(\beta\)-globin polypeptide chain.
In an ideally large, randomly-mating population with no mutation, migration, drift or selection, allele frequencies stay constant. It is disturbed by five factors: gene mutation, gene flow (migration), genetic drift, genetic recombination and natural selection — each a real driver of evolutionary change.
The hominid line, traced mainly from fossils in Africa:
| Form | Note |
|---|---|
| Dryopithecus & Ramapithecus | Ape-like ancestors; Ramapithecus was more man-like |
| Australopithecus | Lived in East African grasslands; ate fruit, ~upright |
| Homo habilis | First tool-maker; brain ~650–800 cc; did not eat meat |
| Homo erectus | Brain ~900 cc; probably ate meat |
| Homo neanderthalensis | Brain ~1400 cc; used hides, buried the dead |
| Homo sapiens | Modern humans; arose in Africa, spread across continents |
1. (NEET PYQ) In a population in Hardy-Weinberg equilibrium, if the frequency of dominant allele p is 0.7, what is the frequency of heterozygotes?
Correct Answer: C. 0.42
Explanation: Since \(p = 0.7\), then \(q = 1 - 0.7 = 0.3\). The heterozygote frequency is \(2pq = 2 \times 0.7 \times 0.3 = 0.42\).