a)High rate of mutation b)Founder effect c)Bottleneck effect d)Cats with extra toes are better at catching mice e)Extra toes are sexually appealing to female cats f)? Q: A high proportion of the cats on Key West have extra toes (polydactyly). The most likely explanation is: How will this population evolve in the future?

Evolutionary Mechanisms Biological evolution: change in genetic composition of a population over time How can the gene pool of a population be characterized quantitatively? What happens to the gene pool of a sexually reproducing population over generations? What mechanisms cause evolutionary change? –Model systems to study evolutionary mechanisms

Quantifying genetic variation in sexually reproducing populations Fig The gene pool is the sum of all alleles Only locus X is shown, with three alleles (X 1, X 2, and X 3 ) Genetic structure is the frequency of the different genotypes in the population.

Allele frequencies Cystic fibrosis is a recessive genetic disease. Among Northern Europeans, the incidence of CF is 1 per 2500 live births. Q1: What is the frequency of the CF allele in the Northern European population? Q2: What proportion of the population are carriers of the CF allele?

Random Mating In Generation II, the allele frequencies are: p = q = For a population in equilibrium: F(AA) = F(Aa) = F(aa) =

Q3 - equilibrium In both populations shown below, p = 0.6 and q = 0.4; which population(s) are in Hardy-Weinberg equilibrium? Population A 36 red (C R C R ), 48 roan (C R C r ), and 16 white (C r C r ). Population B 32 red (C R C R ), 56 roan (C R C r ), 12 white (C r C r ). a.Population A b.Population B c. Both A and B d.Neither A nor B

Hardy-Weinberg (H-W) Equilibrium Assumptions. If the H-W assumptions are met, then allele frequencies will not change from one generation to the next.

HIV infection Is there genetic variation among HIV virus particles in an infected individual? Is there significant mortality in the virus population of an infected individual? Does genetic variation make a difference in survival and reproduction of HIV virus?

HIV prevalence, travel/hiv-and-aids.htm

Numbers of people living with HIV/AIDS WHO/UNAIDS

HIV infection time course

Q4: 3TC resistant viruses a.Arose by mutations induced by 3TC b.Arose from a small pool of mutant viruses already resistant to 3TC c.Arose by gradual adaptation of viruses to 3TC Campbell & Reece 7 th ed. p. 448 Patient No. 1 Patient No. 2 Patient No. 3 Percent of HIV resistant to 3TC Weeks Figure Evolution of Drug Resistance in HIV

Why do anti-HIV drugs become ineffective? Huang et al., 1998, Science 282:1669 Structure of HIV reverse transcriptase & resistance mutations Blue = AZT resistance Lt. Blue = ddI, ddC, 3TC Violet = both AZT + ddI

Origin of Genetic Variation: Mutation Point mutations Insertions/Deletions Inversions/Translocations

Q6: How many times did SIV make the jump to human hosts to become HIV? a.Once b.Twice c.3 times d.4 times e.5 or more

Q7: What anti-HIV therapies are informed by the theory of natural selection? A.Multiple-drug cocktails B.Drug treatment immediately after exposure C.Stopping drug treatment when resistance emerges D.All of the above. E.None of the above.

HIV infects T cells via CD4 and CCR5 cell surface receptors

Frequency of CCR5-delta32 allele in different human populations Northern Europe10% Central Asia 2% Asia, Africa 0% Why is the CCR5-delta 32 allele so frequent among Northern Europeans? Propose at least two alternative hypotheses. What percentage of people in each region are expected to be resistant to HIV infection?