Evolutionary Biology BIOL 3350 Dr Lisa Rapaport Lecture 7 Part 2 Notes and Lecture 8 Part 1 Notes Natural Selection Part 2 I II III Directional selection for A2A2 A A2A2 homozygote has highest fitness B The frequency of the A1 allele will decrease until it becomes extinct under these conditions because the A2 allele has the highest fitness Selection experiment A In the control situation there was no selective pressure for a quicker ability to degrade ethanol the line is basically flat because there is no selective environment changing the frequency In the experimental situations the faster allele rose to fixation very rapidly B C The ADHF alleles were primarily in the heterozygous condition in which they were not having much affect on the population at all but then they rose to fixation in the new environment Natural selection of coat color in pocket mice A B Either homozygous dominant or the heterozygous condition results in In this case the mutant version is dominant a black pocket mouse C The wide type agouti is recessive D The mice that have coat colors that do not match their environment stand out very dramatically E Light colored mice have much higher reflectants F The heterozygous condition has slightly more reflectants than the homozygous dominant condition G The heterozygous condition is slightly different than both homozygous conditions in this situation H Measured it at 6 different sites the shaded areas are the lava flow areas were the substrate is very black I Fixation is nearly reached at the black lava flow sites J The frequency of the dominant allele was nearly at fixation at these K The frequency of the heterozygous mice was lowest at the lava flow L The lava flow sites really select for the dominant homozygous M Shows the frequency of a neutral gene in the last graph as a control group shows that the frequencies showed in the first 3 graphs are in fact caused by coat color and not extraneous factors N Homozygous dominant had the highest fitness in the dark lava flow sites and it had the lowest fitness in the sandy sites lava flow sites sites condition 1 IV Overdominance A A1A2 heterozygote has highest fitness B Both alleles remain in the population over time since the C heterozygous condition has the highest fitness In other cases the less fit genotypes went into extinction but in this case the less fit genotypes stay in the population because both alleles are maintained in the population since the heterozygous condition has the highest fitness D The heterozygous advantage cannot be the only genotype in the population E Overdominance the genotypes that do not have the highest fitness still remain in the population since the heterozygous condition keeps both alleles present Cystic fibrosis A Cystic fibrosis a lethal condition but it continues to remain present V in populations B People who are heterozygous for the cystic fibrosis mutation are C resistant to a bacterium that causes typhoid fever It is advantageous to be heterozygous for the cystic fibrosis mutation because you do not get the cystic fibrosis disease and you are more protected against typhoid fever D This allele will be very deleterious in a population that is not threatened by typhoid fever because then there is not real advantage to being heterozygous for this disease E A typhus environment selects for an allele that would be very deleterious in an environment that does not have typhoid fever as a threat Mean fitness as a function of p for overdominance A The mean population fitness is actually pretty low B When the frequency of the allele A1 is low the mean fitness of the C When the frequency of the allele A1 is high the mean fitness of the D The mean population fitness is at a maximum and equilibrium is E The heterozygous condition has a higher fitness than either population is low population is low as well reached at 0 6 homozygous condition F Since the population is mixed it favors the heterozygous condition because favoring this condition keeps both alleles present neither allele becomes extinct Underdominance A Both homozygotes have higher fitness than heterozygote B If one allele starts out higher than the other allele the initially higher allele will be favored It is only possible to maintain both alleles in the population if their initial frequencies are almost equal or near 0 5 C VI VII 2 D There are natural oscillations every time an oscillation pulls an allele down the other allele will become favored E This equilibrium is unstable as it is not expected to stay in one place F Unstable equilibrium G Either the frequency of compound chromosome 2 or the frequency of compound chromosome 3 went to fixation H This makes sense because of chance fluctuations that occur in the over time population I When a frequency deviates from 0 5 the higher frequency will have reproductive success and survivorship J The initially higher frequency is favored from the beginning VIII Mean fitness as a function of p for underdominance A The mean population fitness is lowest when allele A1 is at about 0 6 B When A1 is low then A2 will be favored and A1 will go to extinction C When A1 is close to fixation the equilibrium will go to fixation in the D Population wide fitness is lowest when the frequency of A1 is at 0 6 E Selection does not always act to give the highest population wide F The population in this case can evolve to fixation at a lower point by other direction fitness chance 3 Agents of Evolution I Mutations as a force of evolution A Mutation provides the raw material for evolution to act B The rate of accumulation is affected by whether the allele is beneficial or deleterious incredibly low rates C A mutation rate of 0 0001 is extremely high mutation rates occur at D Mutations are usually deleterious E The change in the allele frequencies occur at a very slow rate F Irreversible mutations mutations that can only go in one direction 1 2 mutation rate In nature mutations go both ways all of the time G Reversible mutations what it was the loss the gain H Equilibrium 1 P hat equilibrium value of allele A1 2 Q hat equilibrium value of the mutation 3 Since mutations occur at such low frequencies it requires a lot of time to reach equilibrium It takes a very long time for a mutation rate to reach equilibrium I J However other aspects act on populations as well K Many mutations are deleterious so selection acts against them selection works to eliminate harmful mutations from the population Selection A