Chapter 7: Evolution

Q1. State the Hardy-Weinberg principle. What factors disturb it?

Solution

p² + 2pq + q² = 1 (genotype frequencies remain constant across generations)
Factors disturbing H-W equilibrium: (1) Gene flow (2) Genetic drift (3) Mutation (4) Natural selection (5) Non-random mating

Q2. What is the difference between natural selection and artificial selection?

Solution

Natural selection: Nature selects advantageous traits, increases fitness
Artificial selection: Humans select desired traits for breeding (e.g., dog breeds, crop varieties)

Q3. What evidence supports organic evolution?

Solution

1. Fossil record (comparative anatomy)
2. Comparative embryology
3. Biogeography
4. Molecular biology (DNA homology)
5. Vestigial organs

Q4. What is the Miller-Urey experiment?

Solution

Setup: Methane, ammonia, hydrogen, water vapour passed through electric discharge
Result: Amino acids and other organic molecules formed
Demonstrated organic molecules could form from inorganic precursors under primitive Earth conditions

Q5. What is adaptive radiation? Give examples.

Solution

Examples: (1) Darwin's finches - different beak shapes for different food sources (2) Australian marsupials (3) Placental mammals in different continents

Q6. What are the various theories of origin of life?

Solution

Special creation: Created by supernatural power
Spontaneous generation: Life from non-living matter
Biogenesis: Life from pre-existing life
Panspermia: Life from outer space
Chemical evolution: Simple molecules → complex → life (Oparin-Haldane)

Q7. What are the types of natural selection?

Solution

Stabilizing: Favors intermediate phenotype (e.g., human birth weight)
Directional: Favors one extreme (e.g., industrial melanism)
Disruptive: Favors both extremes (e.g., beak size in finches)

Q8. What is industrial melanism?

Solution

Before industrialization: Light moths common (camouflaged on lichen-covered trees)
After industrialization: Dark moths common (soot-covered trees)
Supports natural selection as dark moths had survival advantage

Q9. What are vestigial organs? Give examples.

Solution

Examples: (1) Appendix (2) Wisdom teeth (3) Ear muscles (4) Nictitating membrane (5) Coccyx (tail bone) (6) Body hair

Q10. Describe the stages of human evolution.

Solution

(1) Dryopithecus - ape-like (2) Ramapithecus - more human-like (3) Australopithecus - bipedal (4) Homo habilis - used tools (5) Homo erectus - used fire (6) Homo neanderthalensis - large brain (7) Homo sapiens - modern humans

Q11. What is the difference between homologous and analogous organs?

Solution

Homologous: Same origin, different function (e.g., human hand, whale flipper) - divergent evolution
Analogous: Different origin, same function (e.g., bird wing, insect wing) - convergent evolution

Q12. What is the bottleneck effect?

Solution

Effects: (1) Reduced gene pool (2) Loss of rare alleles (3) Increased homozygosity (4) May lead to inbreeding depression
Example: Northern elephant seal population reduced by hunting

Q13. What is the founder effect?

Solution

Small group isolated from larger population establishes new population with different gene pool
Example: Amish community - high frequency of Ellis-van Creveld syndrome

Q14. What is the Hardy-Weinberg equation?

Solution

p + q = 1 (allele frequencies)
p² + 2pq + q² = 1 (genotype frequencies)
Where: p = dominant allele frequency, q = recessive allele frequency

Q15. What is genetic drift? How is it different from natural selection?

Solution

Genetic drift: Random change in allele frequencies, more in small populations
Natural selection: Differential reproduction based on fitness, directional change
Genetic drift is random; natural selection is based on adaptive advantage

← Chapter 6: Molecular Basis of Inheritance Chapter 8: Human Health and Disease →

← All Class 12 Biology Chapters