A population of beetles shows variation in shell color. After a pesticide treatment, dark-colored beetles survive better. This is an example of:
Answer: B
Directional selection occurs when one extreme phenotype has higher fitness. Dark beetles have selective advantage, shifting population toward darker phenotype.
Q.2Hard
In a gene pool of 500 individuals with allele frequencies p = 0.7 and q = 0.3, how many heterozygous individuals are expected according to Hardy-Weinberg principle?
Which of the following mutations would most likely be lethal?
Answer: C
Loss of an entire chromosome causes imbalance in gene dosage affecting multiple essential genes, making it almost always lethal.
Q.4Hard
Which of the following best explains why antibiotic-resistant bacteria increase in a population after antibiotic exposure?
Answer: C
Pre-existing resistant bacteria survive antibiotic exposure while susceptible ones die, increasing resistant population frequency—natural selection.
Q.5Hard
If a woman with normal vision (but carrier for color blindness) has children with a color-blind man, what percentage of their daughters are expected to have normal vision?
Answer: B
Carrier mother (XBXb) × Color-blind father (XbY) produces: XBXb (carrier daughter), XbXb (color-blind daughter), XBY (normal son), XbY (color-blind son). 50% of daughters (1 out of 2) have normal vision.
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Q.6Hard
Gene flow between two populations can prevent genetic drift from causing fixation of alleles because:
Answer: A
Gene flow (migration) introduces alleles from one population to another, counteracting genetic drift and maintaining genetic variation.
Q.7Hard
A three-point testcross in Drosophila yields recombinant classes with lower frequencies than parental classes. This demonstrates:
Answer: B
Lower recombinant frequencies indicate genes are linked but can undergo crossing over, producing recombinants at lower frequencies than parentals.
Q.8Hard
A lethal allele that causes embryonic death in homozygous condition would alter the expected dihybrid ratio from 9:3:3:1 to:
Answer: A
If one dominant homozygous class (AABB, AABb, or AAbb) is lethal, the 9:3:3:1 ratio adjusts accordingly. Common outcome is 9:3:4 when one class is removed.
Q.9Hard
In humans, if both parents are heterozygous carriers of sickle cell anemia (HbAS), what is the probability of their child being completely unaffected?
Answer: C
Cross: AS × AS produces AA (unaffected, 41), AS (carrier, 21), SS (affected, 41). Probability of unaffected = 41 + 21 = 43 = 0.75
Q.10Hard
The concept of 'adaptive radiation' is best exemplified by:
Answer: A
Darwin's finches underwent adaptive radiation, diverging from a common ancestor into multiple species with different beak morphologies adapted to different food sources.
Q.11Hard
A population experiences a bottleneck reducing its size from 10,000 to 100 individuals. Which evolutionary consequence is MOST likely?
Answer: C
Bottlenecks drastically reduce population size, increasing genetic drift. Random allele loss occurs, reducing genetic variation and increasing chance of fixation.
Q.12Hard
In a X-linked trait, if the allele frequency of the recessive allele in males is 0.1, what is the allele frequency of the recessive allele in females at Hardy-Weinberg equilibrium?
Answer: B
For X-linked traits in males (hemizygous), allele frequency equals phenotype frequency. In females at equilibrium, the allele frequency is the same as in males: 0.1
Q.13Hard
A mutation changes a GC base pair to AT in a non-coding region of DNA. This mutation's evolutionary significance depends primarily on:
Answer: A
Mutations in non-coding regions vary in importance. Those in regulatory elements (promoters, enhancers) can be significant; most others are neutral.
Q.14Hard
A new allele arises in a small island population of 100 individuals. The allele frequency is 0.02. Over the next 10 generations without selection, what is most likely to happen?
Answer: A
In small populations, genetic drift can cause alleles to be randomly lost. With frequency only 0.02 in a population of 100, the allele is vulnerable to random loss.
Q.15Hard
In a three-point testcross involving genes A, B, and C with map distances A-B = 10 map units and B-C = 20 map units, if coefficient of coincidence is 0.8, what is the interference value?
Answer: A
Interference = 1 - Coefficient of Coincidence = 1 - 0.8 = 0.2. This measures how much one crossover interferes with adjacent crossovers.
Q.16Hard
A researcher observes that in a population of snails, shell color is controlled by a single gene with two alleles (B and b). Yellow shells (BB) = 100, Brown shells (Bb) = 300, White shells (bb) = 600. Is this population in Hardy-Weinberg equilibrium?
Answer: B
Total individuals = 1000. p = (200+300)/2000 = 0.25, q = 0.75. Expected: BB = 62.5, Bb = 375, bb = 562.5. Observed shows excess homozygotes, indicating inbreeding or population substructure.
Q.17Hard
Which of the following would NOT cause a change in allele frequencies in a population?
Answer: B
Random assortment of chromosomes during meiosis doesn't change allele frequencies; it only creates different combinations. Selection, drift, and gene flow all change frequencies.
Q.18Hard
A species shows 5 pairs of chromosomes. During meiosis in an individual heterozygous for all 5 genes (AaBbCcDdEe), what is the maximum number of different gamete types that can be produced?
Answer: C
Without crossing over, the number of different gamete types = 2^n, where n = number of heterozygous gene pairs = 2^5 = 32.
Q.19Hard
In a population affected by a recent bottleneck event, which is most likely to occur?
Answer: C
A bottleneck reduces population size dramatically, causing random loss of alleles and making genetic drift the dominant evolutionary force, reducing genetic variation.
Q.20Hard
A researcher studying gene expression notices that identical twins show different phenotypes for a trait despite having identical genotypes. This is most likely due to:
Answer: A
Epigenetic changes (DNA methylation, histone modifications) and differential environmental exposure can cause phenotypic differences in genetically identical individuals.
