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Darwin’s three conditions for natural selection
Trait variation, trait affects fitness, and trait is heritable
What is an adaptation?
A trait favored by natural selection that increases fitness; also the process producing the trait
What constrains adaptations?
Genetic limits, trade-offs, and environmental factors
Define heritability (h²)
Proportion of phenotypic variation due to genetic differences
Heritability formula
h² = VG / VP
Meaning of high heritability (close to 1)
Most variation is genetic; trait is stable across environments
Meaning of low heritability (close to 0)
Most variation is environmental; trait is plastic and can change
Five key evolutionary processes
Mutation, selection, gene flow, genetic drift, nonrandom mating
What is mutation?
Random change in DNA; source of all genetic variation
What is genetic drift?
Random fluctuation in allele frequencies, most significant in small populations
What is a population bottleneck?
Sudden decrease in population size causing loss of genetic diversity and stronger drift
What is the founder effect?
Genetic drift that occurs when a few individuals start a new population
How does gene flow affect variation?
Increases variation within populations and reduces differences between populations
How is heritability measured?
By the slope of a parent-offspring regression line
Why doesn’t natural selection produce “ideal” traits?
Because of constraints like trade-offs, limited variation, and changing environments
Effect of drift on allele frequencies
Drift may fix or eliminate alleles, especially in small populations
What is fixation?
When only one allele remains in a population (frequency = 1)
How do drift and selection interact?
Drift can overpower selection in small populations, even removing beneficial alleles
How does population size affect drift?
Smaller populations experience stronger drift and faster fixation or loss of alleles