The Question is from neet-zoology genetics-evolution mechanism-of-evolution, and it was created by the author K SUNKANNA

Question

A small, isolated island population of finches experiences a drastic reduction in population size due to a volcanic eruption. The surviving finches have a different average beak size compared to the original population. This change is primarily attributed to:

K SUNKANNA · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Population Genetics and Evolutionary Mechanisms
 **Related Topics**: Bottleneck effect, Founder effect, Natural Selection (Directional, Disruptive, Stabilizing)
 **Prerequisites**: Understanding of genetic drift, natural selection, and population size changes.
## SOLUTION PATHWAY
**Given Information**:
  * A small, isolated finch population.
  * A drastic reduction in population size due to a volcanic eruption (a catastrophic event).
  * The surviving finches have a different average beak size than the original population.
**Method & Steps**:
 1. Identify the type of event that caused the population reduction.
  Reasoning: The volcanic eruption drastically reduced the population size, leaving only a small subset of the original population to survive.
  Formula/Rule: None directly applicable, but understanding of population bottleneck is key.
 2. Analyze the impact of this event on the allele frequencies in the surviving population.
  Working: The surviving finches represent a random sample of the original population.  The allele frequencies for beak size are likely to be different in this smaller population compared to the larger original population simply due to chance. This is a random change in allele frequencies.
  Key Point:  The change in average beak size is not necessarily due to natural selection (although it could contribute). It is primarily due to the random loss of genetic diversity.
 3. Determine the most appropriate evolutionary mechanism.
  Result: The bottleneck effect is the best explanation.  A catastrophic event drastically reduced the population size, leading to a random change in the allele frequencies, resulting in a different average beak size.
  Verification:  The other options are less suitable.  The founder effect involves a small group establishing a new population, not a drastic reduction in an existing one. Directional and disruptive selection involve differential reproductive success based on specific traits, not a random reduction in population size.
 ## OPTION ANALYSIS
A :x: Directional selection involves selection for one extreme of a trait, which isn't the primary cause of the change in beak size here.  The change is due to random survival, not selection.
B :x: The founder effect is when a small group establishes a new population. While a similar effect on allele frequency occurs, this scenario is different; it's a drastic reduction of an existing population.
C ✓: The bottleneck effect accurately describes a drastic reduction in population size, leading to a random change in allele frequencies, thus explaining the change in average beak size.
D :x: Disruptive selection favors the extremes of a trait, leading to two distinct phenotypes.  This isn't reflected in the question; there's just a shift in the average beak size.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing bottleneck effect with founder effect: Remember, bottleneck is a drastic reduction in an existing population, while founder effect is the establishment of a new one by a small group.
  2.Attributing the change solely to natural selection:  While natural selection could play a role, the primary cause is the random loss of genetic diversity due to the bottleneck.
 **Quick Tips**:
  1.  Think 'catastrophic event' for bottleneck effect.
  2.  Remember that bottleneck effect leads to reduced genetic diversity.

K SUNKANNA · Answer

Directional selection

K SUNKANNA · Answer

Founder effect

K SUNKANNA · Answer

The correct Option is "Bottleneck effect"

K SUNKANNA · Answer

Disruptive selection

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