Learning Objectives
- Differentiate between Genetic Drift and Natural Selection.
- Identify the roles of the Bottleneck Effect and the Founder Effect in changing allele frequencies.
- Understand how random events versus fitness advantages shape a population’s gene pool.
1. Core Mechanisms of Allelic Change
| Concept | Description | High-Yield Context |
|---|---|---|
| Genetic Drift | A dramatic shift in allelic frequency that occurs by chance rather than natural selection. | Also known as the Wright effect. Includes founder and bottleneck effects. |
| Natural Selection | Alleles that increase species fitness are more likely to be passed down to offspring. | The primary driver of human evolution, fitness, is the deciding factor. |
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2. Types of Genetic Drift (Random Change)
Bottleneck Effect
A natural disaster or catastrophic event removes certain alleles by chance. The resulting population has a new allelic frequency not based on fitness.
Founder Effect
A type of bottleneck occurring due to calamitous population separation. A small group starts a new colony, and their random allele mix becomes the new standard.
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3. Key Comparison
- Genetic Drift: Random, stochastic, and can lead to the loss of beneficial alleles or fixation of harmful ones just by luck.
- Natural Selection: Non-random and directional; it systematically favors traits that improve survival and reproduction.
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