OAT Genetics and Evolution 2 ā Questions and Answers
Question 1: In incomplete dominance, two homozygous parents (red Ć white flowers) produce offspring with pink flowers. When the pink offspring are crossed together, what phenotypic ratio is expected in the F2 generation?
- 3 red : 1 white
- 1 red : 2 pink : 1 white (Correct answer)
- 1 red : 1 white
- All pink
Correct answer: 1 red : 2 pink : 1 white
Crossing heterozygotes (Rr Ć Rr) in an incomplete dominance system yields 1 RR (red) : 2 Rr (pink) : 1 rr (white) because neither allele fully masks the other.
Question 2: Which of the following best describes epistasis?
- Two alleles at the same locus masking each other
- One gene's alleles masking or modifying the expression of a different gene (Correct answer)
- Independent assortment of two unlinked genes
- Crossing over between homologous chromosomes
Correct answer: One gene's alleles masking or modifying the expression of a different gene
Epistasis occurs when the alleles at one gene locus affect the phenotypic expression of a separate gene locus, altering expected Mendelian ratios.
Question 3: What is the Hardy-Weinberg equation used to calculate?
- The rate of mutation in a population
- The expected allele and genotype frequencies in a non-evolving population (Correct answer)
- The number of generations needed for fixation of an allele
- The degree of relatedness between two individuals
Correct answer: The expected allele and genotype frequencies in a non-evolving population
The Hardy-Weinberg equation (pĀ² + 2pq + qĀ² = 1) predicts genotype frequencies under the assumption of no evolution (no selection, drift, gene flow, or mutation).
Question 4: Sickle cell anemia is an autosomal recessive disorder. Two carriers have children together. What fraction of their children would be expected to be carriers but unaffected?
- 1/4
- 1/2 (Correct answer)
- 3/4
- All children
Correct answer: 1/2
A cross between two carriers (Aa Ć Aa) yields 1/4 AA : 2/4 Aa : 1/4 aa; exactly half (2/4) of the offspring are expected to be carriers (Aa) and phenotypically unaffected.
Question 5: Which process generates the greatest genetic diversity during sexual reproduction?
- DNA replication
- Mitosis and cytokinesis
- Independent assortment and crossing over during meiosis (Correct answer)
- Transcription and translation
Correct answer: Independent assortment and crossing over during meiosis
Independent assortment and crossing over during meiosis shuffle alleles into new combinations, producing gametes with unique genetic compositions that drive diversity.
Question 6: According to Darwin's theory of natural selection, which individuals are most likely to contribute offspring to the next generation?
- The largest individuals in the population
- The oldest individuals in the population
- Individuals with traits best suited to their environment (Correct answer)
- Individuals that reproduce asexually
Correct answer: Individuals with traits best suited to their environment
Natural selection favors individuals with heritable traits that increase their reproductive success in their current environment, allowing those traits to increase in frequency.
Question 7: A gene has two alleles with frequencies p = 0.7 and q = 0.3 in a population at Hardy-Weinberg equilibrium. What is the expected frequency of heterozygotes?
- 0.09
- 0.21
- 0.42 (Correct answer)
- 0.49
Correct answer: 0.42
The frequency of heterozygotes is 2pq = 2(0.7)(0.3) = 0.42 according to the Hardy-Weinberg equation.
OAT Genetics and Evolution 2
In incomplete dominance, two homozygous parents (red Ć white flowers) produce offspring with pink flowers.
When the pink offspring are crossed together, what phenotypic ratio is expected in the F2 generation?