Overview
This lecture covers essential key terms from Chapter 19 of Biology 2e, focusing on population evolution, genetics, and mechanisms of evolutionary change.
Population Genetics and Evolution
- Population genetics studies how selective forces change allele frequencies over time.
- Allele frequency (gene frequency) is how often a specific allele appears within a population.
- Gene pool contains all the alleles individuals in a population carry.
- Genetic structure is the distribution of different possible genotypes in a population.
- Genetic variability refers to diversity of alleles and genotypes.
- Population variation is the distribution of phenotypes within a population.
- Geographical variation describes phenotypic differences between populations separated by geography.
Mechanisms of Evolution
- Adaptive evolution is the increase in beneficial alleles and decrease of harmful ones due to selection.
- Genetic drift is the effect of chance on a population’s gene pool.
- Bottleneck effect magnifies genetic drift after natural catastrophes.
- Founder effect occurs when an allele frequency change is started by an isolated subgroup.
- Gene flow is the movement of alleles in and out of a population through migration.
- Nonrandom mating changes a gene pool due to mate choice or other selective forces.
Natural Selection and Fitness
- Evolutionary fitness (Darwinian fitness) is an individual’s ability to survive and reproduce.
- Relative fitness is an individual’s reproductive success compared to the population.
- Selective pressure is any environmental factor making one phenotype more advantageous.
- Stabilizing selection favors average phenotypes.
- Directional selection favors phenotypes at one end of the spectrum.
- Diversifying selection favors two or more distinct phenotypes.
- Frequency-dependent selection favors either common or rare phenotypes.
Sexual Selection and Related Concepts
- Sexual dimorphism is a phenotypic difference between males and females.
- Assortative mating occurs when individuals mate with similar phenotypes.
- Inbreeding is mating between closely related individuals; inbreeding depression increases disease risk.
- Good genes hypothesis suggests individuals display traits signaling genetic quality.
- Handicap principle argues only the fittest can afford costly traits.
- Honest signal is a trait that truthfully shows an individual’s fitness.
Microevolution, Macroevolution, and Modern Synthesis
- Microevolution is change in a population’s genetic structure.
- Macroevolution refers to larger-scale evolutionary changes over long time spans.
- Modern synthesis is the current, widely accepted evolutionary paradigm formed in the 1940s.
- Heritability is the fraction of population variation due to genetic variability.
- Cline is gradual geographic variation across an ecological gradient.
Key Terms & Definitions
- Allele frequency — rate at which a specific allele appears in a population
- Gene pool — all the alleles present in a population
- Genetic drift — random changes in allele frequencies due to chance
- Bottleneck effect — drastic allele frequency change from a natural event
- Founder effect — allele frequency change in a new, isolated group
- Gene flow — movement of alleles between populations
- Stabilizing selection — selection favoring average phenotypes
- Directional selection — selection favoring one extreme phenotype
- Diversifying selection — selection favoring multiple distinct phenotypes
- Sexual dimorphism — physical differences between males and females
- Inbreeding depression — increased rate of abnormalities due to inbreeding
- Heritability — proportion of phenotypic variation caused by genetics
Action Items / Next Steps
- Review all key term definitions for upcoming assessments.
- Read Chapter 19 Summary for broader context of these terms.
- Prepare to answer review and critical thinking questions from the chapter.