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.62Hard
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.63Hard
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.64Hard
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.65Hard
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
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Q.66Hard
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.67Easy
Which of the following best describes the Hardy-Weinberg equilibrium principle?
Answer: A
Hardy-Weinberg equilibrium states that allele frequencies remain constant when no evolutionary forces (mutation, selection, migration, genetic drift) act on a population.
Q.68Easy
In a dihybrid cross between AaBb × AaBb, what is the probability of obtaining aabb genotype?
Answer: A
For AaBb × AaBb, probability of aa = 41 and bb = 41. Combined probability = 41 × 41 = 161.
Q.69Easy
Which type of natural selection favors both extreme phenotypes over the intermediate phenotype?
Answer: A
Disruptive selection eliminates intermediate phenotypes and favors both extreme phenotypes, increasing genetic variation.
Q.70Easy
What is the term for the evolutionary relationship where two or more species share a common ancestor?
Answer: C
Common descent refers to the principle that all organisms share evolutionary ancestry, a fundamental concept in evolutionary biology.
Q.71Medium
In a test cross with a heterozygous individual (Aa), if 40% of offspring show the dominant phenotype, what might this indicate?
Answer: C
In a normal test cross (Aa × aa), expected ratio is 1:1 (50% each). 40% dominant suggests some homozygous dominant (AA) offspring are dying, indicating lethal homozygous dominant allele.
Q.72Medium
Which of the following represents the correct sequence of speciation in peripatric speciation?
Answer: A
Peripatric speciation occurs when a small population is geographically isolated, genetic drift acts strongly, leading to reproductive isolation and speciation.
Q.73Medium
A recessive genetic disorder appears in 1% of a population. What is the frequency of the recessive allele (q)?
Answer: B
If q² = 0.01, then q = √0.01 = 0.1. This is the frequency of the recessive allele.
Q.74Medium
Which mechanism of evolution is most likely responsible for the loss of eyes in blind cave fish?
Answer: B
In cave environments, eyes provide no selective advantage. Neutral mutations affecting eye development accumulate through genetic drift, resulting in eye loss.
Q.75Medium
In Drosophila, if the coefficient of inbreeding (F) increases, what is the expected change in heterozygosity?
Answer: A
Inbreeding increases homozygosity and decreases heterozygosity. The relationship is: Ht = H0(1-F), where heterozygosity decreases with increasing F.
Q.76Medium
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.77Medium
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.78Medium
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.79Medium
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.80Easy
Which of the following is the best evidence for evolution?
Answer: A
Homologous structures (similar structures with different functions) indicate common ancestry and provide strong anatomical evidence for evolution.
