Evolutionary Concepts

Evolution

• Change in allele frequencies over time.

• Traits passed down through generations, increasing in frequency if favorable.

• Can lead to new species.

* 5 modes of evolution: mutation, natural selection, genetic drift, gene flow, sexual selection

Natural Selection

/

• Mechanism of evolution based on favorable/non-favorable traits.

• Affects allele frequencies; leads to reproductive success.

*3 conditions: heritability, differential reproductive success, genetic variation

• genetic variation comes from: sexual reproduction, balanced polymorphism (phenotypes), mutations

Genetic Drift

• Random changes in allele frequencies; can lead to population separation and independent evolution.

• Bottleneck effect: Population reduction due to random events.

• Founder effect: Small group establishes a new population with different allele frequencies.

Factors Influencing Evolution

• Heritability: Traits passed from parents.

• Adaptations: Traits improving survival and reproduction.

• Sexual reproduction: Randomized mix of alleles.

• Gene flow: Incorporation of alleles from one population to another.

• Mutation: Random DNA changes.

• Sexual selection: Traits increasing chances to reproduce in a specific environment.

Types of Natural Selection

• Directional selection: Favors one extreme of a trait spectrum.

• Stabilizing selection: Favors the average trait, extremes are selected against.

• Disruptive selection: Favors both extremes, intermediate traits are selected against.

Sexual Selection

• Females choose, males compete via honest indicators of good genes.

Artificial Selection

• Humans as "agents of natural selection" (e.g., breeding).

Patterns of Evolution

• Coevolution: Mutual evolution between species (e.g., predator/prey).

• Convergent evolution: Unrelated species evolve similar traits due to similar environments.

• Divergent evolution: Related species evolve to become less similar, potentially leading to speciation.

• Parallel evolution: Similar evolutionary changes in different species due to similar environments.

Genetic Variation

• Balanced polymorphism: Multiple phenotypes for a trait.

• Mutation contributes to speciation if variants arise with different phenotypes.

• Heterozygous advantage maintains genetic variance.

• Hybrid vigor maximizes heterozygous genotypes.

• Frequency-dependent selection maintains a balance of phenotypes.

Hardy-Weinberg Equilibrium

• $p + q = 1$ (p = frequency of dominant allele, q = frequency of recessive allele).

• $p^2 + 2pq + q^2 = 1$ ($p^2$ = homozygous dominant frequency, $q^2$ = homozygous recessive frequency, $2pq$ = heterozygous frequency).

• Determines if a population is evolving.

• Conditions: No mutations, no gene flow, no genetic drift (large population), no natural selection, random mating.

Evidence for Evolution

• Homologous characters: Similar traits due to common ancestry.

• Embryology: Similarities in embryos of different organisms.

• Vestigial characters: Structures with little to no function, but useful in ancestors.

Speciation

• Allopatric speciation: Interbreeding ceases due to physical separation leading to independent evolution.

• Sympatric speciation: Interbreeding stops without physical separation.

• Polyploidy: Mutation causing unusual chromosome number, leading to reproductive isolation.

• Adaptive radiation: Rapid speciation events when ancestral species invade new environments.

• Factors include sexual selection, behavioral preferences, and mutations.