Chapter 13: Evolution - Summary of Key Concepts

Fossils and Strata

• Fossils are imprints or remains of organisms that lived in the past (including footprints, burrows, fossilized feces).
• Strata: Layers of sediment that compress to form rock, showing different time periods.
• Relative ages of fossils can be determined from their position in these layers.

Homology and Evolutionary Structures

• Homology: Similarity due to common ancestry.
  • Homologous structures: Different functions but structurally similar.
• Vestigial structures: Remnants of features that served important functions in ancestors.
• Pseudogenes: Genes that have lost their function and are inactive.
• Evolutionary trees: Visual representation of patterns of descent.

Artificial Selection

• Consists of variation and heritability.
• Variation: Breeders select organisms with desirable traits.
• Heritability: Transmission of traits from parent to offspring.

Evolutionary Concepts

• Individuals do not evolve; populations do.
• New alleles arise from mutations in DNA.
• Only mutations in gamete-producing cells affect the population's genetic variability.
• Population: Group of interbreeding individuals of the same species.
• Gene pool: All copies of every allele at every locus in all members of the population.
• Microevolution: Small changes in gene pool.

Hardy-Weinberg Equilibrium

• Equilibrium formula: p + q = 1
• Allele frequencies (e.g., W and w).
• Equation: p^2 + 2pq + q^2 = 1

Causes of Evolutionary Change

• Natural Selection: Mechanism by which only the fittest organisms survive to reproduce.
• Genetic Drift: Random changes in allele frequencies, particularly in small populations.
  • Bottleneck effect: Drastic reduction in population size affecting allele frequencies.
  • Founder effect: New population's gene pool differs from source population.
• Gene Flow: Movement of alleles between populations through individuals or gametes.

Types of Natural Selection

• Directional Selection: Favors individuals at one phenotypic extreme.
• Stabilizing Selection: Favors intermediate phenotypes, reduces extremes.
• Disruptive Selection: Favors extreme phenotypes, leading to contrasting phenotypes.
• Balancing Selection: Maintains stable frequencies of two or more phenotypic forms.
  • Heterozygote advantage: Heterozygous individuals have greater reproductive success.