📑 Topics on this page (Jump to Topic):
📌 1. Mendel & Heredity
- Gregor Johann Mendel — "father of genetics"; experiments on pea (Pisum sativum); 7 contrasting traits. The word "genetics" — Bateson; "gene" — Johannsen.
- Mendel's laws: dominance, segregation (purity of gametes), independent assortment.
- Monohybrid F2 phenotypic ratio 3:1, genotypic 1:2:1; dihybrid F2 — 9:3:3:1. Test cross — F1 × recessive parent.
- Phenotype — visible trait; genotype — genetic make-up (TT, Tt, tt).
📌 2. DNA, RNA, Chromosomes & Sex Determination
| DNA | RNA |
|---|---|
| Double helix — Watson and Crick (1953) | Usually single-stranded |
| Sugar — deoxyribose | Sugar — ribose |
| Bases A, T, G, C | Bases A, U, G, C (uracil replaces thymine) |
| Genetic material | Protein synthesis (mRNA, tRNA, rRNA) |
- Base pairing: A=T (2 hydrogen bonds), G≡C (3 hydrogen bonds). Central dogma: DNA → RNA → protein.
- In humans male XY, female XX; a child's sex is determined by the father's sperm (X or Y).
- Human Genome Project — 1990–2003; humans have about 20,000–25,000 genes. Dolly the sheep (1996) — first mammal cloned from an adult cell. DNA fingerprinting — Alec Jeffreys; in India — Lalji Singh.
📌 3. Evolution
- Lamarck — "inheritance of acquired characters" (giraffe's neck; Philosophie Zoologique, 1809). Weismann refuted it by cutting tails of mice.
- Charles Darwin — natural selection; book "On the Origin of Species" (1859); HMS Beagle voyage, Galápagos finches. The phrase "survival of the fittest" — Herbert Spencer.
- Hugo de Vries — mutation theory (evening primrose).
- Homologous organs — same structure, different function (human arm, bat wing, whale flipper) → divergent evolution. Analogous organs — different structure, same function (bird and insect wings). Vestigial organs in humans — vermiform appendix, wisdom teeth.
- Origin of life: Oparin-Haldane hypothesis; Miller-Urey experiment (1953) — CH₄, NH₃, H₂, water vapour + electric spark gave amino acids. Archaeopteryx — link between reptiles and birds.
⚠️ Exam Traps:
- A baby's sex is determined by the father, not the mother.
- "Survival of the fittest" was coined by Spencer; Darwin adopted it later.
- RNA has uracil, not thymine.
📌 4. Practice MCQs
📝 Practice MCQs (prepared by SF Prep — not PYQs)
Q1. The "father of genetics" is: Practice
Correct answer: (A)
Experiments on pea plants.
Experiments on pea plants.
Q2. Mendel performed his experiments on: Practice
Correct answer: (D)
Pisum sativum.
Pisum sativum.
Q3. The F2 phenotypic ratio of a monohybrid cross is: Practice
Correct answer: (B)
Genotypic ratio 1:2:1.
Genotypic ratio 1:2:1.
Q4. The F2 phenotypic ratio of a dihybrid cross is: Practice
Correct answer: (C)
Evidence for independent assortment.
Evidence for independent assortment.
Q5. The double helix structure of DNA was given by: Practice
Correct answer: (A)
1953; Nobel Prize 1962.
1953; Nobel Prize 1962.
Q6. In RNA, thymine is replaced by: Practice
Correct answer: (C)
RNA sugar is ribose.
RNA sugar is ribose.
Q7. In DNA, guanine pairs with: Practice
Correct answer: (B)
G≡C — three hydrogen bonds.
G≡C — three hydrogen bonds.
Q8. In humans, the sex of a child is determined by: Practice
Correct answer: (D)
Sperm carries X or Y.
Sperm carries X or Y.
Q9. The sex chromosomes of a human male are: Practice
Correct answer: (B)
Female — XX.
Female — XX.
Q10. The term "gene" was coined by: Practice
Correct answer: (D)
In 1909; "genetics" — Bateson.
In 1909; "genetics" — Bateson.
Q11. The first mammal cloned from an adult cell was: Practice
Correct answer: (A)
1996, Scotland (Roslin Institute).
1996, Scotland (Roslin Institute).
Q12. The father of DNA fingerprinting in India is: Practice
Correct answer: (C)
Globally the technique is by Alec Jeffreys.
Globally the technique is by Alec Jeffreys.
Q13. "Inheritance of acquired characters" was proposed by: Practice
Correct answer: (A)
Example of the giraffe's long neck.
Example of the giraffe's long neck.
Q14. "On the Origin of Species" was written by: Practice
Correct answer: (A)
1859; natural selection.
1859; natural selection.
Q15. The mutation theory was given by: Practice
Correct answer: (D)
Studied evening primrose.
Studied evening primrose.
Q16. The phrase "survival of the fittest" was coined by: Practice
Correct answer: (B)
Darwin adopted it in later editions.
Darwin adopted it in later editions.
Q17. The human arm, bat wing and whale flipper are: Practice
Correct answer: (D)
Same structure, different functions.
Same structure, different functions.
Q18. Wings of a bird and an insect are examples of: Practice
Correct answer: (B)
Different structure, same function.
Different structure, same function.
Q19. A vestigial organ in humans is the: Practice
Correct answer: (C)
Wisdom teeth too.
Wisdom teeth too.
Q20. The connecting link between reptiles and birds is: Practice
Correct answer: (C)
Teeth and tail (reptile) + feathers (bird).
Teeth and tail (reptile) + feathers (bird).