A population of beetles shows industrial melanism. Dark beetles increased from 5% to 95% in 50 years in polluted areas. What type of selection is most likely operating?
Answer: B
Industrial melanism is a classic example of directional selection where environmental change (pollution) favors one phenotype (dark color) over another.
Q.42Medium
Which statement about mutations is correct?
Answer: C
Mutations are random, non-directed changes in DNA that provide genetic variation for natural selection to act upon. They're not inherently harmful or beneficial.
Q.43Medium
In a population, the allele frequency of 'a' is 0.4 and 'A' is 0.6. If the population is in Hardy-Weinberg equilibrium, what is the expected frequency of heterozygotes?
Answer: C
Frequency of heterozygotes = 2pq = 2(0.6)(0.4) = 0.48 in Hardy-Weinberg equilibrium.
Q.44Medium
A frameshift mutation occurs in the middle of a gene. What is the most likely consequence?
Answer: C
Frameshift mutations shift the reading frame for all downstream codons, typically resulting in nonfunctional proteins or premature termination.
Q.45Medium
A silent mutation in the third codon position of a gene coding for protein synthesis most likely occurs due to:
Answer: A
The wobble hypothesis explains how changes in the third codon position often don't change the amino acid due to the degeneracy of the genetic code, resulting in silent mutations.
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Q.46Medium
In a testcross of a dihybrid (AaBb) with a homozygous recessive (aabb), if the offspring ratio deviates from 1:1:1:1, it indicates:
Answer: B
A 1:1:1:1 ratio indicates independent assortment. Deviation suggests the genes are linked on the same chromosome, with recombination occurring at a frequency less than 50%.
Q.47Medium
Peppered moths in industrial England showed rapid evolution from predominantly light-colored to dark-colored populations. This is an example of:
Answer: A
Industrial pollution darkened tree bark, favoring dark moths through directional selection. This is a classic example of evolution in response to environmental change.
Q.48Medium
A mutation converts an amino acid codon (GUU for valine) to a stop codon (UAA). This type of mutation would most severely affect the protein by:
Answer: B
A nonsense mutation (codon to stop codon) causes premature termination of translation, resulting in a truncated, usually nonfunctional protein. This is more severe than missense mutations.
Q.49Medium
In a cross between two heterozygous individuals (Aa × Aa), if the homozygous dominant genotype (AA) is lethal and dies in utero, the surviving offspring ratio would be:
Answer: B
Aa × Aa normally produces 1 AA : 2 Aa : 1 aa. If AA is lethal, only Aa and aa survive in a 2:1 ratio.
