Heredity = transmission of traits from parents to offspring via genes. Evolution = change in inherited traits over generations. AMU asks 2–3 MCQs — focus on Mendel's ratios, sex determination, homologous vs analogous organs, Darwin's natural selection, and fossil evidence.
1) Basic genetics — key terms
| Term | Definition |
|---|---|
| Gene | Segment of DNA coding for a specific trait; basic unit of heredity |
| Allele | Alternate form of a gene (e.g. T = tall, t = short) |
| Genotype | Genetic makeup (e.g. TT, Tt, tt) |
| Phenotype | Observable trait (e.g. tall, short) |
| Homozygous | Two identical alleles (TT or tt) — pure |
| Heterozygous | Two different alleles (Tt) — hybrid |
| Dominant | Allele expressed even with a different allele present (T) |
| Recessive | Allele expressed only when homozygous (tt) |
2) Mendel's experiments
Gregor Mendel (Father of Genetics) — worked on garden pea (Pisum sativum) for 7 years.
Why pea? Easy to grow, true-breeding lines, controlled mating, 7 clear traits with contrasting forms, large offspring numbers.
Why pea? Easy to grow, true-breeding lines, controlled mating, 7 clear traits with contrasting forms, large offspring numbers.
2.1 Monohybrid cross (1 trait)
P: TT (Tall) × tt (Short)
F₁: All Tt (Tall — dominant)
F₁ self (Tt × Tt):
F₁: All Tt (Tall — dominant)
F₁ self (Tt × Tt):
Punnett → 1 TT : 2 Tt : 1 tt
Genotypic ratio: 1:2:1
Phenotypic ratio: 3 Tall : 1 Short
Law of Dominance: In heterozygote, dominant allele masks recessive. F₁ all show dominant trait.
Law of Segregation: Alleles separate during gamete formation → each gamete gets one allele → recessive trait reappears in F₂ (3:1).
Law of Segregation: Alleles separate during gamete formation → each gamete gets one allele → recessive trait reappears in F₂ (3:1).
2.2 Dihybrid cross (2 traits)
P: RRYY (Round Yellow) × rryy (Wrinkled Green)
F₁: All RrYy (Round Yellow)
F₁ self (RrYy × RrYy): 9 Round Yellow : 3 Round Green : 3 Wrinkled Yellow : 1 Wrinkled Green
Phenotypic ratio: 9:3:3:1
F₁: All RrYy (Round Yellow)
F₁ self (RrYy × RrYy): 9 Round Yellow : 3 Round Green : 3 Wrinkled Yellow : 1 Wrinkled Green
Phenotypic ratio: 9:3:3:1
Law of Independent Assortment: Alleles of different traits segregate independently during gamete formation (applies when genes are on different chromosomes).
🔥 AMU PYQ: Monohybrid F₂ phenotypic ratio is:
(A) 3:1 (B) 1:2:1 (C) 9:3:3:1 (D) 1:1 Ans: A
(A) 3:1 (B) 1:2:1 (C) 9:3:3:1 (D) 1:1 Ans: A
🔥 AMU PYQ: Dihybrid F₂ phenotypic ratio is:
(A) 3:1 (B) 1:2:1 (C) 9:3:3:1 (D) 9:7 Ans: C
(A) 3:1 (B) 1:2:1 (C) 9:3:3:1 (D) 9:7 Ans: C
3) Sex determination
Humans: 22 pairs autosomes + 1 pair sex chromosomes.
• Female: XX (homogametic) — all eggs carry X.
• Male: XY (heterogametic) — sperm 50% X, 50% Y.
• Sex determined by father — X + X = girl; X + Y = boy. 50% probability each.
• SRY gene on Y chromosome triggers male development.
• Other systems: Birds (ZZ-ZW: male ZZ, female ZW), Grasshoppers (XX-XO: male XO), Bees (haplodiploid: unfertilized → haploid male).
• Female: XX (homogametic) — all eggs carry X.
• Male: XY (heterogametic) — sperm 50% X, 50% Y.
• Sex determined by father — X + X = girl; X + Y = boy. 50% probability each.
• SRY gene on Y chromosome triggers male development.
• Other systems: Birds (ZZ-ZW: male ZZ, female ZW), Grasshoppers (XX-XO: male XO), Bees (haplodiploid: unfertilized → haploid male).
🔥 AMU PYQ: In humans, sex of child is determined by:
(A) Mother (B) Father (C) Both (D) Environment Ans: B
(A) Mother (B) Father (C) Both (D) Environment Ans: B
4) Evolution — theories
4.1 Lamarck's theory
• Use and disuse: Organs used more become stronger; unused degenerate.
• Inheritance of acquired characters: Changes during lifetime passed to offspring.
• Example: Giraffe's long neck (stretching → inherited).
• Rejected — Weismann showed acquired characters aren't inherited (cut mice tails for 20 gen → tails still present).
• Inheritance of acquired characters: Changes during lifetime passed to offspring.
• Example: Giraffe's long neck (stretching → inherited).
• Rejected — Weismann showed acquired characters aren't inherited (cut mice tails for 20 gen → tails still present).
4.2 Darwin's theory (Natural Selection)
• Key points: Overproduction → Limited resources → Struggle for existence → Variation → Natural selection (survival of the fittest) → Inheritance of favourable traits → Speciation over generations.
• Darwin's finches (Galapagos) — 13 species from common ancestor, different beak shapes for different food → adaptive radiation.
• Published "On the Origin of Species" (1859).
• Darwin's finches (Galapagos) — 13 species from common ancestor, different beak shapes for different food → adaptive radiation.
• Published "On the Origin of Species" (1859).
4.3 Modern synthetic theory (Neo-Darwinism)
Integrates Darwin's natural selection with genetics. Key factors: Mutations (source of variation), Genetic recombination (crossing over, independent assortment), Gene flow (migration), Genetic drift (random changes, especially small populations), Natural selection, Geographical isolation (speciation).
5) Evidences of evolution
| Evidence | Description | Examples |
|---|---|---|
| Homologous organs | Same basic structure, different functions → divergent evolution (common ancestor) | Forelimbs of humans, bats, whales, horses — same pentadactyl pattern, different uses |
| Analogous organs | Different structure, same function → convergent evolution | Wings of birds, bats, insects; eyes of vertebrates & octopus |
| Vestigial organs | Functional in ancestors but reduced/lost function now | Human appendix, coccyx, wisdom teeth, nictitating membrane; pelvic bones in whales & pythons |
| Fossils | Preserved remains of ancient organisms | Archaeopteryx (reptile → bird transition — teeth, feathers, claws); Horse evolution series (Eohippus → Equus) |
| Embryology | Similar early developmental stages across related groups | All vertebrate embryos have pharyngeal arches, tail, notochord → common ancestor |
| Molecular (DNA) | DNA/protein sequence comparison shows relatedness | Human & chimpanzee DNA ≈ 98.5% identical; Cytochrome c differences correlate with evolutionary distance |
🔥 AMU PYQ: Forelimbs of humans and bats are:
(A) Analogous (B) Homologous (C) Vestigial (D) Fossil Ans: B
(A) Analogous (B) Homologous (C) Vestigial (D) Fossil Ans: B
🔥 AMU PYQ: Archaeopteryx is a link between:
(A) Reptiles & birds (B) Fish & amphibians (C) Amphibians & reptiles (D) Birds & mammals Ans: A
(A) Reptiles & birds (B) Fish & amphibians (C) Amphibians & reptiles (D) Birds & mammals Ans: A
6) Speciation
Speciation = formation of new species. Steps: Geographic isolation → No gene flow → Genetic divergence (mutation, selection, drift) → Reproductive isolation → New species.
• Allopatric: With geographical isolation (most common).
• Sympatric: Without geographical isolation (e.g. polyploidy in plants).
• Allopatric: With geographical isolation (most common).
• Sympatric: Without geographical isolation (e.g. polyploidy in plants).
7) Human evolution
| Species | Time | Key features |
|---|---|---|
| Australopithecus ("Lucy") | ~3.9 mya | Bipedal, small brain (400–500 cc), Ethiopia |
| Homo habilis | ~2.8 mya | First Homo, brain ~600–800 cc, used stone tools (Oldowan) |
| Homo erectus | ~2 mya | First to use fire, larger brain, migrated out of Africa (Java/Peking Man) |
| Homo neanderthalensis | ~400,000 ya | Large brain, complex tools, buried dead, interbred with modern humans |
| Homo sapiens | ~300,000 ya | Modern humans, advanced language/art/culture, Out of Africa migration |
8) AMU PYQs — quick revision
Q1. Mendel is known as:
(A) Father of Medicine (B) Father of Genetics (C) Father of Evolution (D) Father of Biology Ans: B
(A) Father of Medicine (B) Father of Genetics (C) Father of Evolution (D) Father of Biology Ans: B
Q2. In pea plants, yellow (Y) is dominant over green (y). F₂ of YY × yy gives:
(A) 3 Yellow : 1 Green (B) 1:2:1 (C) 9:3:3:1 (D) 1:1 Ans: A
(A) 3 Yellow : 1 Green (B) 1:2:1 (C) 9:3:3:1 (D) 1:1 Ans: A
Q3. Wings of bird and insect are:
(A) Homologous (B) Analogous (C) Vestigial (D) None Ans: B
(A) Homologous (B) Analogous (C) Vestigial (D) None Ans: B
Q4. Human appendix is a:
(A) Homologous organ (B) Analogous organ (C) Vestigial organ (D) Vital organ Ans: C
(A) Homologous organ (B) Analogous organ (C) Vestigial organ (D) Vital organ Ans: C
Q5. Darwin's theory is based on:
(A) Mutation (B) Natural selection (C) Acquired characters (D) Genetic drift Ans: B
(A) Mutation (B) Natural selection (C) Acquired characters (D) Genetic drift Ans: B
Q6. The number of autosomes in a normal human male is:
(A) 44 (B) 46 (C) 45 (D) 22 Ans: A
(A) 44 (B) 46 (C) 45 (D) 22 Ans: A
Q7. Correct human evolution order:
(A) Australopithecus → Homo habilis → Homo erectus → Homo sapiens Ans: A
(A) Australopithecus → Homo habilis → Homo erectus → Homo sapiens Ans: A
Q8. First human species to use fire:
(A) Homo habilis (B) Homo erectus (C) Neanderthal (D) Australopithecus Ans: B
(A) Homo habilis (B) Homo erectus (C) Neanderthal (D) Australopithecus Ans: B
Q9. Which is NOT a Mendelian trait in pea?
(A) Pod colour (B) Seed colour (C) Flower colour (D) Leaf shape Ans: D
(A) Pod colour (B) Seed colour (C) Flower colour (D) Leaf shape Ans: D
Q10. The fittest organisms survive and reproduce — this is called:
(A) Mutation (B) Natural selection (C) Genetic drift (D) Speciation Ans: B
(A) Mutation (B) Natural selection (C) Genetic drift (D) Speciation Ans: B
Q11. Miller-Urey experiment produced:
(A) Amino acids (B) Proteins (C) DNA (D) Cells Ans: A
(A) Amino acids (B) Proteins (C) DNA (D) Cells Ans: A
Q12. All vertebrate embryos have gill slits in early stages → evidence of:
(A) Convergent evolution (B) Common ancestry (C) Lamarckism (D) Genetic drift Ans: B
(A) Convergent evolution (B) Common ancestry (C) Lamarckism (D) Genetic drift Ans: B
📝 Pro Tip for AMU: Monohybrid = 3:1 (phenotypic), 1:2:1 (genotypic). Dihybrid = 9:3:3:1. Sex: XX = female, XY = male; father determines sex. Homologous (same structure) vs Analogous (same function). Darwin = natural selection. Archaeopteryx = reptile → bird. Fossils = direct evidence. Homo erectus = first to use fire.