Mechanisms of Evolution

Reindeer from a rancher in Alaska escape from their pen during an enormous snow storm. After their escape, they mate with wild caribou that are migrating across the land. The offspring of these have traits for short legs and have tame behavior.

• Gene Flow

• Genetic Drift

• Non-Random Mating

• Natural Selection

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Males of the bighorn sheep species fight one another to show females who is the dominant male and are more likely to mate with females.

• Natural Selection

• Mutation

• Genetic Drift

• Non-Random Mating

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During a hurricane, a population of beetles almost gets completely wiped out. The only beetles that survived were lucky that they were in their nest at the time of the hurricane and had enough food to survive.

• Natural selection

• Genetic Drift

• Gene Flow

• Non-Random Mating

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A chemical spill causes a genetic change in the offspring of ladybugs to have blue dots instead of black dots.

• Natural Selection

• Genetic Drift

• Mutation

• Gene Flow

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Insects become resistant to pesticides very quickly, sometime in one generation. If an insect is resistant to the chemical, most of the offspring will also be resistant. Considering that insect generations can be a matter of weeks, insects in an area can become immune to a chemical within months.

• Mutation

• Natural Selection

• Genetic Drift

• Gene Flow

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This is the pattern of natural selection where BOTH of the extreme versions of a trait are more advantageous than the average, so a population evolves in both directions away from the average

• Directional Selection

• Disruptive Selection

• Stabilizing Selection

• Radical Selection

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This is a pattern of natural selection where one extreme form of a trait is more advantageous than the average or the opposite extreme; as a result, this trait in the population tends to evolve towards that one extreme

• Directional selection

• Disruptive selection

• Stabilizing selection

• Forward selection

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This is the process that ultimately creates new variations and changes in DNA; leads to the creation of new alleles

• Mutation

• Microevolution

• Natural selection

• Gene flow / genetic drift

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This is a pattern of natural selection in which the average (or intermediate) form of a trait is the most advantageous, and so a population evolves away from the extremes and toward the average

• Disruptive selection

• Directional selection

• Stabilizing selection

• Middle selection

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Why is the mouse population changing over time?

• The light mice can reproduce more successfully than the dark mice

• The hawks eat more dark mice than light mice because the dark mice taste better

• The hawks eat more light mice than dark mice because they can see the light mice more easily

• The hawks eat more dark mice than light mice because they can see the dark mice more easily

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