ap bio chapter 21: Concept 21.3: Natural selection, genetic drift, and gene flow can alter allele frequencies in a population

What is natural selection?

Differential reproductive success that leads to certain alleles being passed to the next generation in greater proportions.

How does natural selection affect allele frequency?

Advantageous traits increase in frequency over generations.

What is an example of natural selection in action?

DDT-resistant insects survived pesticide use and passed on their resistance, leading to a population with more resistant individuals.

What is genetic drift?

A change in allele frequencies due to chance events, especially in small populations.

Why does genetic drift have a bigger impact on small populations?

Smaller populations are more affected by random changes, which can significantly alter allele frequencies.

What is an example of genetic drift?

A mudslide kills most fish in a small lake, leaving only a few survivors by chance, altering allele frequencies.

What is the founder effect?

When a small group of individuals becomes isolated from the main population, leading to a different allele frequency by chance.

How does the founder effect impact genetic diversity?

It reduces genetic variation because the new population starts with only a small subset of alleles.

What is an example of the founder effect?

A storm blows a few birds onto an island, where they start a new population with different allele frequencies than the original.

What is the bottleneck effect?

A drastic reduction in population size due to an environmental change, leading to a loss of genetic diversity.

Why does the bottleneck effect reduce genetic variation?

Only a few individuals survive, meaning many alleles are lost from the gene pool.

What is an example of the bottleneck effect?

Overhunting reduces a big cat population from 10,000 to 300, eliminating many alleles and forcing inbreeding.

How does genetic drift affect populations?

It can randomly change allele frequencies and lead to loss of genetic variation.

Why can genetic drift be harmful?

Harmful alleles can become fixed if they are the only ones left after a random event.

What are two major examples of genetic drift?

The founder effect and the bottleneck effect.

What is gene flow?

The movement of alleles between populations through migration or the transfer of gametes.

How does gene flow affect genetic variation?

It tends to reduce differences between populations by mixing alleles.

What is an example of gene flow in plants?

Pollen carried by wind or pollinators spreads alleles between different plant populations.

How can gene flow decrease fitness?

If an organism immigrates and introduces maladaptive traits, survival in the new environment may decrease.

How can gene flow increase fitness?

If alleles for insecticide resistance spread in mosquitoes, they survive better in areas with insecticides.

How is gene flow affecting modern human populations?

Increased mixing of genetic traits through migration is influencing characteristics like skin color.

Why is gene flow important in human evolution?

It introduces new genetic diversity, which can lead to changes over generations.