lecture 2- evolution and natural selection

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19 Terms

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Darwin’s three conditions for natural selection

Trait variation, trait affects fitness, and trait is heritable

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What is an adaptation?

A trait favored by natural selection that increases fitness; also the process producing the trait

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What constrains adaptations?

Genetic limits, trade-offs, and environmental factors

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Define heritability (h²)

Proportion of phenotypic variation due to genetic differences

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Heritability formula

h² = VG / VP

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Meaning of high heritability (close to 1)

Most variation is genetic; trait is stable across environments

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Meaning of low heritability (close to 0)

Most variation is environmental; trait is plastic and can change

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Five key evolutionary processes

Mutation, selection, gene flow, genetic drift, nonrandom mating

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What is mutation?

Random change in DNA; source of all genetic variation

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What is genetic drift?

Random fluctuation in allele frequencies, most significant in small populations

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What is a population bottleneck?

Sudden decrease in population size causing loss of genetic diversity and stronger drift

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What is the founder effect?

Genetic drift that occurs when a few individuals start a new population

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How does gene flow affect variation?

Increases variation within populations and reduces differences between populations

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How is heritability measured?

By the slope of a parent-offspring regression line

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Why doesn’t natural selection produce “ideal” traits?

Because of constraints like trade-offs, limited variation, and changing environments

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Effect of drift on allele frequencies

Drift may fix or eliminate alleles, especially in small populations

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What is fixation?

When only one allele remains in a population (frequency = 1)

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How do drift and selection interact?

Drift can overpower selection in small populations, even removing beneficial alleles

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How does population size affect drift?

Smaller populations experience stronger drift and faster fixation or loss of alleles