AGENTS OF EVOLUTIONPowerPoint PresentationSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16AGENTS OF EVOLUTIONI. Mutations as a force of evolutionA. Mutations create new alleles1. Introduces variation at the level of the gene∆F508+ to ∆F5 08µ = 6.7 x 10-7B. How effective is mutation as an evolutionary force?1. Weak forcefor rapid evolutionarychangeA aC. Modeling mutation1. Irreversible mutations-forward mutation only-no back or reverse mutations occurA a = µCalculating frequency of mutant allele with known mutation rate µ-initial frequency in a diploid population = 1/2N-with known mutation rate µ, can calculate allele frequency for any generation (t):pt = p0 (1 - µ)t2. Reversible Mutations-forward mutations (A to a) at a rate of µ decrease frequency of p. -backward or reverse mutations (a to A) at a rate of vpt = pt-1 - µpt-1 + qt-1vAaµv3. Equilibrium-forward mutation rate = backward mutation ratep = v q = µ µ + v µ + v^ ^t0pt01µ = 10-4v = 10-5p = 0.091^20,00050,000Requires 100s to 1000s of generations to reach equilibriumII. Mutation-Selection BalanceA. Most mutations are deleterious1. Selection works to eliminate these alleles in populations2. Recurrent mutation continues to introduce these alleles in populations.EQUILIBRIUM:Rate of introduction (mutation) = Rate of elimination (selection)B. What is the frequency of a deleterious recessive at equilibrium?1. Mutation favors a (mutation wants this)2. Selection favors Aw11 = 1.0 w12 = 1.0 w22 = 1.0 - sA a = µp 1.0p 0.0q =√ µsqt01s = 0.01, µ = 10-4 ^s = 0.1, µ = 10-9 When q is recessiveC. What is the frequency of a deleterious dominant at equilibrium?1. Mutation favors dominant A22. Selection favors recessive A1w11 = 1.0 w12 = 1.0 - s w22 = 1.0 - sA1 A2 = µp 1.0p 0.0q = µsqt01s = 0.01, µ = 10-4 ^s = 0.1, µ = 10-9 When q is dominantD. Mutation is most effective in increasing q, when q is recessiveE. Mutation-selection balance maintains deleterious recessive traits1. Especially true when heterozygotes have superior fitness (overdominance)-cystic fibrosis allele, heterozygote advantage during typhoid fever epidemics-sickle-cell anemia, heterozygote advantage in regions with malariaHeterozygotes are resistant to typhoid fever bacteriumS. typhi selects for overdominance at ∆F508