8.1 Micro Evolution

• Sickle Cell Anemia affects 1 in 25 people in Africa. Results in an abnormal RBC shape (sickle). Caused by a recessive allele
• If homozygous recessive for SCA = have SCA
• If heterozygous for SCA = don’t have SCA and resistant to Malaria
• Sickle cell allele high in areas where

  Malaria is high
• Darwin couldn’t explain how variations (the basis of Natural Selection) pass from one generation to the

  next. Mendel solved the inheritance piece of the puzzle
• Mendel and Darwin lived at the same time yet knew nothing of each other‘s work.
• Gene Pool: All the alleles in the individuals that make up a population
• Sources of Variation:

  • Mutation
  • Sexual Reproduction
• Mutation: Change in DNA sequence

  • Due to mistakes or env.
  • Some don’t change phenotype
  • Affects organisms fitness
• Sexual Reproduction: Variation due to scrambling of alleles

  • Differences among individuals due to sexual recombination
• Hardy-Weinberg Equilibrium:

  1. Random Mating
  2. Large Population
  3. No movement in/out of the population (NO gene flow)
  4. No mutations
  5. No Natural Selection
• 3 Types of Selective Pressure that can account for Natural Selection:

  1. Stabilizing Selection
  2. Directional Selection
  3. Disruptive Selection
• Sexual Selection: Form of Natural Selection in which individuals

  with certain traits are more likely to obtain mates than others. Mating is often not random
• Artificial Selection: Intentional breeding to produce certain traits in a population.
• Unlike Artificial Selection and Natural

  Selection, Genetic Drift is random! Change in gene pool due to chance.
• Genetic Drift Types:

  1. Bottleneck Effect
  2. Founder Effect
• Bottleneck Effect: A reduction in the gene pool due to a sudden reduction in the population size (eg. natural disasters).
• Loss of variation results in a decreased ability of a population to adapt to environment change because of such small numbers
• Founder Effect: The process by which a small number of individuals from a population found a new habitat and established a new population.
• Gene Flow: The movement of alleles from one population to another.