pace and if evolution is occurring

OTHER MEANS OF EVOLUTION

  • Module 2 of Moodle contains materials and resources focused on Chapters 4 & 5 in the textbook.

  • Important to answer Moodle chapter questions for credit.

LEARNING OBJECTIVES

  • Genetic Drift: Understand how it works and its effects on populations.

  • Natural Selection: Compare and contrast it with genetic drift.

  • Hardy-Weinberg Principle: Work through related problems and understand equilibrium requirements.

  • Evolution Models: Discuss punctuated equilibrium and gradualism.

  • Natural Selection Types: Identify and provide examples of disruptive, directional, and stabilizing selection.

  • Neutral Theory: Describe it and explain the molecular clock connection.

EVOLUTION SOURCES

  • Populations, not individuals, evolve; this is indicated by a change in allelic frequency.

  • Allele: A segment of DNA coding for a gene that impacts traits.

  • Evolution: Change in allelic frequency over time.

FIVE AGENTS OF EVOLUTIONARY CHANGE

  1. Mutation

    • Ultimate source of variation; occurs rarely.

  2. Gene Flow

    • Movement of individuals/gametes between populations.

  3. Nonrandom Mating (e.g., inbreeding)

    • Alters genotype percentages without changing allele frequency.

  4. Genetic Drift

    • Statistical accidents leading to random changes in allele frequencies, more pronounced in small populations.

  5. Selection

    • The only agent causing adaptive evolutionary changes.

HOW EVOLUTION OCCURS

  • Emigration & Immigration: Changes allelic frequency based on gene variations.

    • Example: Pollen variation influencing flower color.

  • Nonrandom Mating:

    • Leads to sexual selection where certain traits increase mating success. Females control mate selection due to the value of eggs versus sperm.

GENETIC DRIFT

  • Alters allele prevalence significantly in small populations due to random events (founder's effect).

POPULATION STABILITY AND EVOLUTION

  • Equilibrium: Populations stable, not evolving.

  • Natural Selection drives change through selective pressure adapting organisms to the environment.

  • Genetic Drift causes random changes irrespective of environmental factors.

HARDY-WEINBERG PRINCIPLE

  1. Conditions for Equilibrium:

    • No mutation.

    • No gene transfer (immigration/emigration).

    • Random mating.

    • Large population size.

    • No selection occurs.

  2. Hardy-Weinberg Equation:

    • p² + 2pq + q² = 1 (where p = dominant allele, q = recessive allele).

  3. Application: Changes can suggest hypotheses about evolutionary processes in populations not meeting these conditions.

PRACTICAL EXAMPLES

  • Sickle-Cell Anemia:

    • SS (normal), ss (sickle-cell), Ss (heterozygous and more resistant to malaria).

    • If 9% of population are ss, calculate heterozygous frequency using the 2pq term.

  • Mice Example:

    • A lab population with 35% white mice (aa). Determine allelic and genotypic frequencies through q².

NATURAL SELECTION AS EVOLUTION DRIVING FORCE

  • Example: Beak size in birds influenced by seed availability causing changes in allelic frequency.

TYPES OF SELECTION

  • Stabilizing Selection: Favors moderate traits, trims extremes.

  • Directional Selection: Favors one extreme trait, shifts population trait frequencies.

  • Disruptive Selection: Favors both extremes over moderate traits.

ADAPTIVE SELECTION THEORY

  • Emphasizes change in environments and how it affects allelic frequency.

NEUTRAL THEORY OF EVOLUTION

  • Polymorphism Maintenance: Achieved through the balance of mutation and genetic drift.

  • Many mutations are neutral, with little effect on fitness revealed over time.

MOLECULAR CLOCK CONCEPT

  • Frequency of neutral mutations offers insights into evolutionary time scales.

  • Neutral mutations accumulate at a consistent rate across species.

GRADUALISM VS. PUNCTUATED EQUILIBRIUM

  • Gradualism involves slow, steady change over time.

  • Punctuated equilibrium proposes rapid changes interspersed with long periods of stability.

STUDY QUESTIONS

  1. Explain the molecular clock and its biological importance.

  2. Compare and contrast the neutral theory and adaptive selection theory.

  3. Describe gradualism and punctuated equilibrium differences.

  4. Define Hardy-Weinberg equilibrium.

  5. Solve a Hardy-Weinberg problem using the provided equations.