GENETICS & EVOLUTION – FREQUENTLY ASKED QUESTIONS (WITH ANSWERS)
CLASS 12 BIOLOGY
✅ 1. What is genetics?
Answer:
Genetics is the branch of biology that deals with the study of heredity and variation.
✅ 2. What is heredity?
Answer:
Heredity is the transmission of traits or characters from parents to offspring.
✅ 3. What is variation?
Answer:
Variation refers to differences in traits among individuals of the same species.
✅ 4. Who is called the Father of Genetics?
Answer:
Gregor Johann Mendel.
✅ 5. What is a gene?
Answer:
A gene is a segment of DNA that controls the expression of a character.
✅ 6. What are alleles?
Answer:
Different forms of the same gene controlling a particular trait.
✅ 7. What is genotype?
Answer:
Genotype is the genetic constitution of an individual (e.g., TT, Tt).
✅ 8. What is phenotype?
Answer:
Phenotype is the visible expression of a gene (e.g., tall, dwarf).
✅ 9. What is Mendel’s Law of Segregation?
Answer:
During gamete formation, alleles of a gene separate out so each gamete receives only one allele.
✅ 10. What is Mendel’s Law of Independent Assortment?
Answer:
Genes for different traits separate independently during gamete formation.
✅ 11. What is a monohybrid cross?
Answer:
A cross involving one character (e.g., tall × dwarf).
✅ 12. What is a dihybrid cross?
Answer:
A cross involving two characters (e.g., seed shape and seed color).
✅ 13. What is a test cross?
Answer:
Crossing an F1 hybrid with a homozygous recessive parent.
✅ 14. What is incomplete dominance? Give example.
Answer:
Neither allele is completely dominant; results in intermediate phenotype.
Example: Snapdragon flower – Red × White → Pink.
✅ 15. What is codominance? Give example.
Answer:
Both alleles express equally in the phenotype.
Example: AB blood group (IA and IB are codominant).
✅ 16. What is multiple allelism?
Answer:
A gene that has more than two alleles.
Example: ABO blood group: IA, IB, i.
✅ 17. What is polygenic inheritance?
Answer:
Traits controlled by multiple genes.
Example: Human skin colour, height.
✅ 18. What is sex-linked inheritance?
Answer:
Inheritance of traits controlled by genes located on sex chromosomes.
Example: Color blindness.
✅ 19. What is mutation?
Answer:
Sudden and heritable change in DNA sequence.
✅ 20. What is evolution?
Answer:
Gradual change in living organisms over generations.
✅ 21. Name the scientist who proposed Natural Selection.
Answer:
Charles Darwin.
✅ 22. What is natural selection?
Answer:
The process by which organisms better adapted to their environment survive and reproduce.
✅ 23. What is genetic drift?
Answer:
Random changes in allele frequency in small populations.
✅ 24. What is Hardy–Weinberg principle?
Answer:
Allele frequencies in a population remain constant unless disturbed by evolutionary forces.
✅ 25. What is gene flow?
Answer:
Movement of genes between populations through migration.
✅ 26. What are fossils?
Answer:
Preserved remains or traces of ancient organisms.
✅ 27. What is speciation?
Answer:
Formation of new species from existing ones.
✅ 28. What are homologous organs?
Answer:
Structures with similar origin but different functions.
Example: human arm & bat wing.
✅ 29. What are analogous organs?
Answer:
Structures with different origin but same function.
Example: wings of bird & insect.
✅ 30. What is adaptive radiation?
Answer:
Evolution of different species from a common ancestor in different environments.
Example: Darwin’s finches.
GENETICS & EVOLUTION – 10 LONG QUESTIONS WITH ANSWERS
✅ 1. Explain Mendel’s monohybrid cross. Describe the Law of Segregation.
Answer:
A monohybrid cross involves one trait.
Example: Tall (TT) × Dwarf (tt) pea plants.
F1 Generation:
All tall (Tt) because tall (T) is dominant.
Selfing of F1:
Tt × Tt → F2 ratio:
Phenotype: 3 Tall : 1 Dwarf
Genotype: 1 TT : 2 Tt : 1 tt
Law of Segregation:
Alleles separate during gamete formation, so each gamete gets only one allele. Recessive traits reappear in F2.
✅ 2. Describe Mendel’s dihybrid cross and explain the Law of Independent Assortment.
Answer:
Mendel studied two traits: Seed shape (Round vs Wrinkled) and seed colour (Yellow vs Green).
Cross:
RRYY × rryy → F1: RrYy (all Round Yellow)
Selfing of F1:
F2 phenotypic ratio = 9:3:3:1
(Round Yellow : Round Green : Wrinkled Yellow : Wrinkled Green)
Law of Independent Assortment:
Alleles of different genes assort independently during gamete formation. One trait does not affect inheritance of another.
✅ 3. Explain incomplete dominance with an example.
Answer:
Incomplete dominance occurs when neither allele is fully dominant.
Example: Snapdragon flower
RR (Red) × rr (White) → F1: Rr (Pink)
F2 ratio:
Phenotypic: 1 Red : 2 Pink : 1 White
Genotypic: 1 RR : 2 Rr : 1 rr
This shows blending in appearance but not in genotype.
✅ 4. Describe codominance and multiple allelism with the example of ABO blood group.
Answer:
Codominance:
Both alleles express equally.
Example: IA and IB → Blood group AB.
Multiple Allelism:
A gene having more than two alleles.
ABO: IA, IB, i
Genotypes:
A = IAIA or IAi
B = IBIB or IBi
AB = IAIB
O = ii
Shows both codominance and multiple alleles.
✅ 5. Describe sex-linked inheritance with examples.
Answer:
Traits controlled by genes on sex chromosomes (X or Y).
X-linked diseases:
Colour blindness
Haemophilia
Duchenne muscular dystrophy
Colour blindness cross:
Carrier mother (XᴺXᶜ) × Normal father (XᴺY)
Sons have 50% chance of colour blindness.
Sex-linked traits appear more in males because they have only one X chromosome.
✅ 6. Explain the structure of DNA and its salient features.
Answer:
DNA is a double helix formed by two antiparallel strands.
Components:
Sugar: Deoxyribose
Phosphate
Nitrogen bases: A, T, G, C
Base pairing (Chargaff):
A = T
G = C
Through hydrogen bonds.
Features:
Double-stranded
Helical structure
Genetic material
Capable of replication
Carries hereditary information
✅ 7. Describe Darwin’s theory of natural selection.
Answer:
Darwin proposed that evolution occurs due to natural selection.
Main points:
Overproduction: Organisms produce more offspring than needed.
Variation: Individuals show differences.
Struggle for existence: Compete for food, space, mates.
Survival of the fittest: Best-adapted survive.
Natural selection: These survivors reproduce more.
Speciation: Over time, new species form.
Example: Evolution of long neck in giraffes.
✅ 8. Explain Hardy–Weinberg principle and its significance.
Answer:
Hardy–Weinberg principle states that allele frequencies remain constant in a population if no evolutionary force acts.
Equation:
p + q = 1
p² + 2pq + q² = 1
Where:
p² = homozygous dominant
2pq = heterozygous
q² = homozygous recessive
Conditions:
No mutation
No migration
Large population
Random mating
No natural selection
Used for predicting gene frequencies.
✅ 9. Describe the different evidences of evolution.
Answer:
1. Paleontological Evidence:
Fossils show progression of life forms.
2. Homologous Organs:
Same origin, different functions.
Example: forelimbs of humans and whales.
3. Analogous Organs:
Different origin but same function.
Example: wings of birds & insects.
4. Embryological Evidence:
Embryos of different animals show similarities.
5. Molecular Evidence:
Similar DNA, proteins suggest common ancestry.
✅ 10. Explain genetic drift. Describe the Founder effect and Bottleneck effect.
Answer:
Genetic drift is the random change in allele frequencies in small populations.
Two major types:
1. Founder Effect
A few individuals start a new population.
Allele frequency differs from original population.
Example: Amish population showing Ellis-Van Creveld syndrome.
2. Bottleneck Effect
Sudden reduction in population due to natural disaster.
Remaining population has different genetic frequency.
Genetic drift reduces variation and impacts evolution.
