Genetic drift, bottleneck effect and founder effect | Biology | Khan Academy

Definition of Evolution: The change in heritable traits of a population over generations.
Key Concept: Often conflated with Natural Selection; however, Natural Selection is just one mechanism of evolution.

Mechanism of Evolution: Focuses on variation in heritable traits within a population.
Traits: Different traits can provide advantages for survival and reproduction.
- Example Traits: Color variations in circles (blue, magenta, yellow).
Process: Traits that are more fit for the environment (e.g., blue circles being less likely to be caught by predators) tend to reproduce at higher rates, leading to a dominant allele in the population over generations.

Definition: Another mechanism of evolution; describes random changes in allele frequencies in a population.
Random Changes: Unlike Natural Selection, it does not favor traits based on environmental suitability; rather, changes occur by chance.
Example with Rabbits:
- Population of 10 rabbits with two alleles for color: dominant (B) for brown and recessive (b) for white.
- No survival advantage for either phenotype leads to random allele reproduction.
- Subsequent generations may show increased frequency of a particular allele due to random chance.

Likelihood: More pronounced in small populations; larger populations dilute the effects of genetic drift.
Consequences: Can lead to loss of genetic diversity and potential loss of favorable traits.

Definition: Occurs after a significant reduction in population size due to an event (e.g., natural disasters).
Impact: Only a few individuals survive, leading to reduced genetic variation.
- Example: A bottle pouring out marbles—only a small selection survives, representing a loss of diversity.

Definition: Occurs when a small group from a larger population starts a new population.
Characteristics: May result in a population with less genetic variation; the founding members may not represent the genetic diversity of the original population.
- Example: Two blue characters leaving their population and establishing a new one, which may lack other alleles or traits.

Key Takeaway: While Natural Selection emphasizes environmental fitness in evolution, Genetic Drift focuses on random chance occurrences that impact allele frequencies and population variation. Both processes play significant roles in the overall pattern of evolution.