Natural Selection / Mechanisms of Evolution

What is directional selection?

Selection that favors one extreme phenotype, causing the population distribution to shift toward that extreme.

What is stabilizing selection?

Selection that favors intermediate phenotypes and selects against extremes.

What is disruptive selection?

Selection that favors both extreme phenotypes and selects against intermediate phenotypes.

What happens to a graph during directional selection?

The distribution shifts toward one extreme.

What happens to a graph during stabilizing selection?

The distribution becomes narrower around the average.

What happens to a graph during disruptive selection?

The distribution becomes more bimodal, with peaks at both extremes.

What are the three major mechanisms of evolution?

Natural selection, genetic drift, and gene flow.

What is genetic drift?

Random changes in allele frequencies due to chance.

Is genetic drift adaptive?

No. It is random with respect to fitness.

What is gene flow?

The movement of alleles between populations through migration and reproduction.

Is gene flow adaptive?

Generally, no. The movement of alleles itself is not driven by differences in fitness.

Which mechanism of evolution is directly associated with differential reproductive success?

Natural selection

Which mechanism is random?

Genetic drift.

Which mechanism involves migration?

Gene flow

Which mechanism can increase genetic diversity within a population?

Gene flow

Which mechanism commonly decreases genetic diversity?

Genetic drift.

How does population size affect genetic drift?

Genetic drift has a stronger effect in small populations.