Evolution and Its Processes

Four Processes of Evolution

Evolution is the change in the genetic composition of a population over time. Four main processes drive evolutionary change:

• Natural Selection: The process by which individuals with advantageous traits survive and reproduce more successfully, leading to adaptation.

• Genetic Drift: Random changes in allele frequencies, especially in small populations. Includes the founder effect and bottleneck effect.

• Gene Flow: Movement of alleles between populations through migration, increasing genetic diversity.

• Mutation: The source of new genetic variation; changes in DNA sequence can introduce new alleles.

Example: The peppered moth population in England changed color due to natural selection during the Industrial Revolution.

Key Terms in Evolution

• Evolution: Change in heritable traits in a population across generations.

• Fossils: Preserved remains or traces of organisms, providing evidence for evolution.

• Adaptations: Traits that enhance survival and reproduction.

• Homology/Homologous Structures: Similar structures due to shared ancestry (e.g., vertebrate limbs).

• Analogy/Analogous Structures: Similar functions but different evolutionary origins (e.g., wings of birds and insects).

• Vestigial Structures: Remnants of features that served a function in ancestors (e.g., human appendix).

• Convergent Evolution: Independent evolution of similar traits in unrelated lineages.

• Gene Pool: All alleles present in a population.

• Adaptive Evolution: Evolution that results in a better fit between organisms and their environment.

• Fitness: The reproductive success of an individual relative to others.

Genetic Drift: Founder and Bottleneck Effects

• Founder Effect: When a few individuals colonize a new area, their gene pool may differ from the original population.

• Bottleneck Effect: A sudden reduction in population size leads to loss of genetic diversity.

Types of Selection

• Directional Selection: Favors one extreme phenotype.

• Disruptive Selection: Favors both extreme phenotypes.

• Stabilizing Selection: Favors intermediate phenotypes.

• Sexual Selection: Selection for traits related to mating success.

• Sexual Dimorphism: Differences in appearance between males and females.

Speciation and Species Concepts

Mechanisms of Speciation

Speciation is the process by which new species arise. It can occur via different mechanisms:

• Allopatric Speciation: Occurs when populations are geographically isolated.

• Sympatric Speciation: Occurs without geographic isolation, often via polyploidy or habitat differentiation.

• Adaptive Radiations: Rapid evolution of multiple species from a common ancestor, often after colonizing new environments.

Species Concepts

• Biological Species Concept: Species are groups of interbreeding natural populations that are reproductively isolated from other groups.

• Morphological Species Concept: Species are defined by physical traits.

• Ecological Species Concept: Species are defined by their ecological niche.

• Phylogenetic Species Concept: Species are the smallest group sharing a common ancestor.

Reproductive Isolation and Barriers

• Prezygotic Barriers: Prevent mating or fertilization.

  • Habitat Isolation: Populations live in different habitats.

  • Temporal Isolation: Populations breed at different times.

  • Behavioral Isolation: Differences in mating behaviors.

  • Mechanical Isolation: Physical incompatibility.

  • Gametic Isolation: Gametes cannot fuse.

• Postzygotic Barriers: Prevent hybrid offspring from surviving or reproducing.

  • Reduced Hybrid Viability: Hybrids do not develop properly.

  • Reduced Hybrid Fertility: Hybrids are sterile.

  • Hybrid Breakdown: Hybrids' offspring are weak or sterile.

Phylogeny and Classification

Phylogeny and Taxonomy

Phylogeny is the evolutionary history of a species or group. Taxonomy is the science of naming and classifying organisms.

• Taxon: A group of organisms at any level of classification.

• Phylogenetic Tree: Diagram showing evolutionary relationships.

  • Branch Point: Represents divergence of two lineages.

  • Sister Taxa: Groups that share an immediate common ancestor.

  • Basal Taxon: Lineage that diverged early.

Types of Phylogenetic Trees

• Monophyletic: Includes ancestor and all descendants.

• Paraphyletic: Includes ancestor and some, but not all, descendants.

• Polyphyletic: Includes taxa with different ancestors.

Domains of Life: Bacteria, Archaea, and Eukarya

Key Differences Between Domains

The three domains of life are distinguished by cellular structure, genetic material, and metabolic pathways.

Diversity and Transmission of Genetic Material

• Bacteria: Exchange genetic material via plasmids, transformation (uptake of DNA), transduction (virus-mediated), and conjugation (cell-to-cell transfer).

• Archaea: Similar mechanisms to bacteria, but with unique genetic features.

• Eukarya: Genetic material transmitted through sexual reproduction and cell division.

Bacterial Structure and Metabolism

Bacterial Cell Features

• Gram Staining: Differentiates bacteria by cell wall structure.

  • Gram-Positive: Thick peptidoglycan wall, stains purple.

  • Gram-Negative: Thin peptidoglycan wall, outer membrane, stains pink.

• Bacterial Capsule: Protective layer outside cell wall.

• Bacterial Endospores: Resistant structures for survival in harsh conditions.

• Nucleoid: Region containing bacterial DNA.

• Plasmid: Small, circular DNA molecules.

Bacterial Reproduction and Genetic Exchange

• Binary Fission: Asexual reproduction by cell division.

• Transformation: Uptake of foreign DNA from environment.

• Transduction: Transfer of DNA via bacteriophages.

• Conjugation: Direct transfer of DNA between cells.

Bacterial Metabolism

• Obligate Aerobes: Require oxygen for metabolism.

• Obligate Anaerobes: Cannot tolerate oxygen.

• Facultative Anaerobes: Can use oxygen or not.

Archaea: Unique Features

Extremophiles

• Extreme Halophiles: Thrive in high salt environments.

• Extreme Thermophiles: Thrive in high temperature environments.

• Methanogens: Produce methane, often in anaerobic conditions.

Metabolic Substrates and Nutrition

Substrates of Metabolism

• Autotrophs: Use inorganic carbon (CO2) as carbon source.

• Heterotrophs: Use organic carbon sources.

• Mixotrophs: Can use both inorganic and organic carbon sources.

Substrate Availability by Domain

Symbiosis and Ecological Relationships

Types of Symbiosis

• Mutualism: Both partners benefit.

• Commensalism: One benefits, other unaffected.

• Parasitism: One benefits, other harmed.

• Pathogens: Disease-causing organisms.

Summary Table: Key Terms and Concepts

Additional info: Academic context was added to expand brief points into full explanations, and tables were inferred for clarity. These notes cover chapters 22, 23, 24, 26, and 27, focusing on evolution, speciation, phylogeny, and the domains of life.