Genes, Chromosomes, etc.

The tiny mechanisms of evolution

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Evolution at the Population Level

Gene Flow The Movement of Alleles

The Movement of AllelesMigration and Inter-breeding

Genetic Drift Random change in gene pool,

particularly powerful in small populations

Genetic Drift

Genetic Drift and Population Size

Founder Effect Small number of individuals from population

migrate and form new population May not carry all alleles in parent population May carry alleles in different frequencies

from parent population

Bottleneck Effect Catastrophic events (floods, diseases)

leave a few survivors Survivors may not carry all alleles in

parent population May carry alleles in different

frequencies from parent population

The Bottleneck Effect

Forces of Evolution and Genetic Variation

Evolutionary Force

Variation within population

Variation between populations

Mutation Increases Increases

Gene Flow Increases Decreases

Genetic Drift Decreases Increases

Natural Selection

Decreases or stabilizes

Increases

Speciation and Forces of Evolution Time

› Mutation and natural selection produce change over time

› Enough time (and change) leads to appearance of new “kind”

Reproductive isolation› No gene flow to reduce differences

between populations› Mutations, genetic drift, and natural

selection increase differences