GED Science TestLife ScienceHard
A group of scientists is studying a population of Galapagos finches. They observe that during a prolonged drought, finches with larger, stronger beaks are better able to crack open the tough seeds that are still available, while finches with smaller beaks struggle to find food. Over several generations, the average beak size in the population increases. This is an example of:
- AGene Flow
- BGenetic Drift
- CDirectional Selection
- DStabilizing Selection
Show answer & explanationAnswer & explanation
Correct answer: C. Directional Selection
Directional selection occurs when individuals at one end of the phenotypic range have higher fitness than individuals in the middle or at the other end. In this case, larger beaks confer a survival advantage during drought, shifting the average beak size towards the larger end of the spectrum over time.
Why the other options are wrong
- A. Gene flow is the movement of alleles between populations, not selective pressure within a population.
- B. Genetic drift is random changes in allele frequencies, more pronounced in small populations, not due to selective pressure.
- D. Stabilizing selection favors intermediate phenotypes and acts against extreme variations, which is the opposite of the scenario described.
Directional Selection
Directional selection is a mode of natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype.
- Favors one extreme of the phenotypic range.
- Leads to a shift in the population's average trait value.
- Common in environments undergoing change.
- Example: increasing beak size in finches during drought.
Memory trick: Directional goes one way, Stabilizing stays the same, Disruptive splits apart!