The chapter “Evolution” is fundamental for CBSE as well as competitive exams because it connects variation, heredity, and population genetics to explain how allele frequencies change over generations. Topics like Hardy–Weinberg equilibrium, inbreeding, selection, genetic drift, speciation mechanisms, and molecular evolution concepts (neutral theory, ) are frequently tested both for conceptual understanding and for numerical problem-solving.
20
Minutes
15
Questions
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Marking
Q1. In a large randomly mating population in Hardy–Weinberg equilibrium the frequency of a recessive phenotype is (i.e. ). What is the expected frequency of heterozygotes () in this population?
Q2. A diploid population has allele frequencies and . Viability selection acts with fitnesses . Using the selection recurrence
(where is mean fitness), what is the allele frequency after one generation of selection?
Q3. In a randomly mating population the autosomal recessive disease has affected frequency . If inbreeding increases so that the inbreeding coefficient is , what is the expected frequency of carriers (heterozygotes)? (Use .)
Q4. Assertion (A): Under neutral theory the substitution rate (rate of molecular evolution) equals the neutral mutation rate and is independent of effective population size .
Reason (R): The number of new neutral mutations per generation is approximately , but the fixation probability of a single neutral mutation is about , so the substitution rate per generation equals .
Both A and R are true, but R does not explain A.
Both A and R are true and R explains A.
A is true but R is false.
A is false but R is true.
Q5. Consider an infinitely large panmictic population with two alleles A and a where . The internal equilibrium is given by . If the initial frequency of A is , what is the long-term outcome under selection (no mutation, migration or drift)?
Allele a will be fixed because .
A stable polymorphism with will be maintained.
Allele A will be fixed.
Allele a will be fixed because is the lowest fitness.
Q6. In a large randomly mating population under Hardy–Weinberg equilibrium the frequency of the homozygous recessive genotype () is . What is the expected frequency of heterozygotes ()?
Q7. On an island the allele has frequency . Each generation, a fraction of individuals are migrants from the mainland where . Using , what is the allele frequency of on the island after one generation of migration (ignore selection and drift)?
Q8. Consider four taxa A, B, C, D with binary characters (1 = derived, 0 = ancestral) as follows: A: , B: , C: , D: . Which of the following unrooted trees is the most parsimonious (requires the fewest character changes)?
((A,B),(C,D))
((A,C),(B,D))
((A,B),(C,D)) and ((A,D),(B,C)) are equally most parsimonious
((A,D),(B,C))
Q9. Two allopatric populations diverged from an ancestor fixed for . In population I allele arose and fixed (population genotype ); in population II allele arose and fixed (population genotype ). Assume Dobzhansky–Muller incompatibility occurs only when both derived alleles are homozygous together () and that heterozygotes are viable. Which cross will produce some inviable offspring expressing the incompatibility?
F1 hybrids produced by crossing population I × population II
F2 generation from selfing F1 individuals
Backcross of an F1 to the parent population
Backcross of an F1 to the parent population
Q10. A completely recessive deleterious allele has mutation rate and selection coefficient against homozygotes in a population with effective size . Which statement is correct?
Genetic drift will dominate allele dynamics because .
Mutation–selection balance predicts .
Both drift and selection will influence dynamics since , and mutation–selection predicts .
The allele will be rapidly eliminated because selection is much stronger than drift.
Q11. In a large random‑mating population the allele frequencies at a locus are and . Expected heterozygosity under Hardy–Weinberg is . A sample shows observed heterozygosity . Using , estimate the inbreeding coefficient (rounded to two decimal places).
0.04
0.14
0.86
0.25
Q12. In a large panmictic population allele has frequency and allele has . Fitnesses are , , . Using
calculate the allele frequency of after one generation of selection (rounded to three decimal places).
0.600
0.675
0.391
0.641
Q13. A large panmictic population is in Hardy–Weinberg equilibrium with allele frequency . Assuming no evolutionary forces act, what will be the expected frequency of heterozygotes after two generations?
0.48
0.32
0.16
0.60
Q14. Assertion (A): Genetic drift can cause rapid fixation or loss of neutral alleles in small populations, contributing to genetic divergence between isolated populations. Reason (R): The strength of genetic drift increases with effective population size because sampling fluctuations are larger in bigger populations.
Which of the following is correct?
Both A and R are true, and R correctly explains A.
Both A and R are true, but R does not explain A.
A is true but R is false.
A is false but R is true.
Q15. Assertion (A): For a protein‑coding gene, a ratio (nonsynonymous to synonymous substitution rate) is generally interpreted as evidence of positive selection on that gene. Reason (R): A raised ratio can also arise from relaxed purifying selection or increased fixation of slightly deleterious nonsynonymous mutations in populations with reduced effective size , not only from positive selection.
Which of the following is correct?
Both A and R are true, and R correctly explains A.
Both A and R are true, but R does not explain A.
A is true but R is false.
A is false but R is true.