Microevolution in Finches & Anoles (HHMI Videos) Finches: Microevolution is observed through changes in beak size and shape due to environmental press

Microevolution in Finches & Anoles (HHMI Videos)

• Finches: Microevolution is observed through changes in beak size and shape due to environmental pressures like drought or food availability. Natural selection favors finches with beak types best suited to available food sources.

• Anoles: Adaptations in limb length and toe pad size in response to different habitats (e.g., tree-dwelling vs. ground-dwelling) show microevolutionary changes over generations.

Smallest Unit That Can Evolve

• A Population

  • Individuals do not evolve; evolution occurs across generations in populations as allele frequencies change due to natural selection, mutation, genetic drift, etc.

Homologous Structures

• Term: Homologous Structures

  • Structures with a similar build due to common ancestry but may have different functions (e.g., whale flippers and human hands).

Vestigial Structures

• Definition: A homologous structure that has lost its function in one organism (e.g., human appendix, whale pelvic bones).

Other Types of Homologies

1. Molecular Homologies: Similarities in DNA/protein sequences among species.

2. Developmental Homologies: Similar embryonic development patterns across different species.

Biogeographical Evidence for Evolution

• Definition: The study of the geographic distribution of species.

• How it helps: Explains how isolated species (e.g., Galápagos finches) evolve differently from their mainland relatives due to environmental pressures.

Hardy-Weinberg Equilibrium Conditions

1. Large population size (no genetic drift)

2. No mutations

3. No natural selection

4. Random mating

5. No gene flow (immigration/emigration)

Hardy-Weinberg Problem: 75% Dominant Phenotype

• p² + 2pq = 0.75, q² = 0.25, q = 0.5, p = 0.5

• Heterozygous individuals (2pq) = 2(0.5)(0.5) = 0.50 or 50%

• Homozygous recessive (q² = 0.25) → 0.25 × 1000 = 250 individuals

Matching Genetic Terms

1. Gene Pool → (e) The sum of all alleles in a population.

2. Genetic Drift → (f) A random change in the allelic frequencies of a population.

3. Natural Selection → (c) The process by which traits that are beneficial become more common over time.

4. Founder Effect → (b) A group moves to a new location, and their gene frequencies differ from the source population.

5. Bottleneck Effect → (d) A large portion of a population is killed, altering gene frequencies.

6. Mutation → (a) A change in an organism’s DNA.

7. Gene Flow → (g) Genetic exchange between populations.

Two Main Causes of Genetic Variation

1. Mutation: Creates new alleles.

2. Recombination (Sexual Reproduction): Shuffles alleles during meiosis and fertilization.

Multiple Choice Practice

1. (A) Greater in small populations.

2. (B) On islands (isolated populations).

3. (C) High number of offspring surviving to reproductive age.

4. (C) p² + 2pq represents dominant phenotype frequency.

5. (A) Biogeography (distribution of species).

6. (A) Directional selection (shift toward one extreme trait).

Hardy-Weinberg Practice

• Given aa (q²) = 36% (0.36)

  • q = √0.36 = 0.6

  • p = 1 - q = 0.4

  • AA (p²) = (0.4)² = 0.16 (16%)

  • Aa (2pq) = 2(0.4)(0.6) = 0.48 (48%)

  • AA + Aa (dominant phenotype) = 16% + 48% = 64%

Butterfly Population Problem

• White butterflies (bb) = 40% → q² = 0.40 → q = √0.40 = 0.63

• p = 1 - q = 1 - 0.63 = 0.37

• Heterozygous (2pq) = 2(0.37)(0.63) = 0.47 or 47%

• Homozygous dominant (p²) = (0.37)² = 0.14 or 14%

PTC Tasting Problem

• q² = 65/215 = 0.302 → q = √0.302 = 0.55

• p = 1 - q = 0.45

• p² (TT) = (0.45)² = 0.202 or 20.2%

• 2pq (Tt) = 2(0.45)(0.55) = 0.495 or 49.5%

• q² (tt) = 30.2% (given)