Evolution 6: Measuring Evolution

Mutation:

  • Mutation creates variation

  • New mutations are constantly appearing

  • Mutation changes DNA sequence, changes amino acid sequence, changes protein structure and function, changes traits, changes fitness (maybe)

Gene Flow

  • Movement of individuals and alleles in and out of population

  • seed pollen distribution by wind/insects

  • migration of animals

  • reduces differences between populations

  • gene flow in human pops increasing today due to modern travel

Non random mating

  • Sexual selection

Genetic Drift

  • Effect of chance events; founder event, bottlenecks

  • Loss of alleles from gene pool: reduces variation, reduces adaptability

Natural Selection

  • Differential survival and reproduction due to changing environmental conditions

  • Combinations of alleles that provide “fitness” increase in the pop

  • Adaptive evolutionary change

What conditions cause allele frequencies not to change?

Hardy-Weinburg Equilibrium

  • Describes Hypothetical, non-evolving that preserves allele frequencies

  • Serves as model for comparison (null hypothesis)

  • Natural populations never in H-W equilibrium

Formulas:

p+q=1

p² + 2pq + q² = 1

H-W theorem:

  • assume two alleles = B,b

  • frequency of dominant allele (B) = p

  • frequency of recessive allele (b) = q

Frequencies must add to 1 (100%), so:

                            p + q = 1

  • frequency of homozygous dominant: p x p = p²

  • frequency of homozygous recessive: q x q = q²

  • frequency of heterozygotes: (p x q) + (q x p) = 2pq

  • frequency of all individuals: p² + 2pq + q² = 1

Steps:

  1. Write both equations

  2. Identify any given info

  3. Don’t screw up frequencies

    1. remember that sqrt of decimal is larger # than that decimal

  4. First: figure out q. q is the magic key that lets you unlock the other variables in the equations

  5. Work around problem till all terms solved for

  6. Practice makes perfect