BIOL140 Lecture 5: Hardy-Weinberg and Adaptive Evolution:

Hardy-Weinberg Principle:

• Equations:

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

  • p² + 2pq + q² = 1 (genotype frequencies: p² = homozygous dominant, 2pq = heterozygous, q² = homozygous recessive)

• Assumptions for Equilibrium:

  • No mutation, no migration, large population, random mating, and no selection.

• An example with black and speckled seals is used to calculate allele and genotype frequencies.

Why Do Populations Change?

• Adaptive Evolution: Natural selection drives adaptation.

• Non-Adaptive Evolution: Genetic drift, migration, mutations.

Natural Selection:

• Mechanism of Evolution: Traits that improve survival and reproduction are passed down.

• Darwin and Wallace: Developed the theory of natural selection, with Darwin’s On the Origin of Species published in 1859.

• 3 Requirements for Natural Selection:

  1. Heritable traits.

  2. Variation in traits.

  3. Consequences for reproduction due to these variations.

Types of Selection:

• Directional Selection: One extreme is favored (e.g., green katydids favored for camouflage).

• Stabilizing Selection: The average is favored (e.g., human birth weights).

• Disruptive Selection: Both extremes are favored (e.g., light and dark oyster shells).

Example: Peahens prefer peacocks with large, colorful tails, illustrating directional selection (sexual selection).

Artificial Selection:

• Selective Breeding by Humans: Alters species for desired traits.

  • Example: Brassica oleracea (wild cabbage) selectively bred into broccoli, cauliflower, kale, etc.

  • Dr. Gina Fernandez’s Research: Uses genetic markers to breed strawberries with specific flavors, disease resistance, and appearance.

  • Consequences: Human selection has drastically altered plant and animal genetics.

Rapid Evolution and Modern Relevance:

• Pharmaceuticals vs. Evolution: Pathogens like MRSA evolve resistance quickly due to short generation times, forcing continuous drug development.

Learning Objectives:

1. Define Natural Selection: Mechanism for evolutionary change through differential reproductive success.

2. Discuss Selection Types: Directional, stabilizing, and disruptive selection.