Population Genetics

Page
3

Slide 21

Slide 22

Microevolution of Species

Slide 23

Causes of Microevolution

Genetic Drift

- the change in the gene pool of a small population due to chance

Natural Selection

- success in reproduction based on heritable traits results in selected alleles being passed to relatively more offspring (Darwinian inheritance)

- Cause ADAPTATION of Populations

Gene Flow

-is genetic exchange due to the migration of fertile individuals or gametes between populations

Slide 24

Causes of Microevolution

Mutation

a change in an organism’s DNA

Mutations can be transmitted in gametes to offspring

Non-random mating

- Mates are chosen on the basis of the best traits

Slide 25

Genetic Drift

Slide 26

Factors that Cause Genetic Drift

Bottleneck Effect

a drastic reduction in population (volcanoes, earthquakes, landslides …)

Reduced genetic variation

Smaller population may not be able to adapt to new selection pressures

Founder Effect

occurs when a new colony is started by a few members of the original population

Reduced genetic variation

May lead to speciation

Slide 27

Slide 28

Loss of Genetic Variation

Cheetahs have little genetic variation in their gene pool

This can probably be attributed to a population bottleneck they experienced around 10,000 years ago, barely avoiding extinction at the end of the last ice age

Slide 29

Slide 30

Founder’s Effect

Slide 31

Modes of Natural Selection

Slide 32

Modes of Natural Selection

Directional Selection

Favors individuals at one end of the phenotypic range

Most common during times of environmental change or when moving to new habitats

Disruptive selection

Favors extreme over intermediate phenotypes