Argumentation
A few birds colonize an isolated island. By chance, the founding birds carry an allele at a much higher frequency than the mainland population. Which process is most directly illustrated?
- AFounder effect, a form of genetic driftcorrect
- BTranslation of mRNA into a protein
- CDirectional selection caused by a measured fitness advantage
- DHydrolysis of a polysaccharide
Why A is correct
The founder effect occurs when a small founding group has allele frequencies that differ by chance from the source population.
The stem asks students to explain a specific mechanism, not just recall a unit term: "A few birds colonize an isolated island. By chance, the founding birds carry an allele at a much higher frequency...". The correct choice is supported by The founder effect occurs when a small founding group has allele frequencies that differ by chance from the source population. The tempting alternatives such as Translation of mRNA into a protein or Directional selection caused by a measured fitness advantage fail because they do not produce the same outcome described in the stem.
Argumentation · with figure
In a population, individuals heterozygous for allele H survive a parasite outbreak better than either homozygote. Which claim is best supported?
- AHeterozygote advantage can maintain genetic variationcorrect
- BSelection acts only against heterozygotes
- CAcquired changes in body condition are sufficient evidence that allele frequencies changed.
- DThe population must be in Hardy-Weinberg equilibrium during the outbreak.
Why A is correct
If heterozygotes have higher fitness than either homozygote, selection can maintain both alleles in the population. This is a form of balancing selection.
The evidence in the prompt matters before the topic label: "In a population, individuals heterozygous for allele H survive a parasite outbreak better than either homozygote....". The supported answer is "Balancing selection may maintain both alleles because heterozygotes have the..." because If heterozygotes have higher fitness than either homozygote, selection can maintain both alleles in the population. Distractors such as Allele H must disappear immediately because selection acts only... or Acquired changes in body condition are sufficient evidence that... either ignore the stated pattern or name a related concept without matching the evidence.
Argumentation · with figure
A population has the expected allele frequencies for Hardy-Weinberg calculations, but individuals preferentially mate with others that have similar phenotypes. Which claim is best supported by the genotype data?
- AThe observed counts show no difference between homozygotes and heterozygotes.
- BAssortative mating must increase heterozygotes in every case.
- CHeterozygotes are lower than expected while homozygotes are highercorrect
- DThe data exactly match Hardy-Weinberg genotype expectations.
Why C is correct
The observed data show fewer heterozygotes and more homozygotes than expected under random mating. This pattern is consistent with assortative mating by similar phenotype.
The evidence in the prompt matters before the topic label: "A population has the expected allele frequencies for Hardy-Weinberg calculations, but individuals preferentially...". The supported answer is "observed deficit of heterozygotes is consistent with nonrandom mating" because This pattern is consistent with assortative mating by similar phenotype. Distractors such as observed counts show no difference between homozygotes and heterozygotes or Assortative mating must increase heterozygotes in every case either ignore the stated pattern or name a related concept without matching the evidence.