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Date Created: 04/27/14
Evolution by natural selection Tuesday April 15 ZD14 738 PM Chapter 253 The Process of Evolution How does Natural Selection Work Darwin39s Inspiration 0 Pigeon breeding crossbreeding of desired traits artificial selection 0 An Essay on the Principles of Population by Thomas Robert Malthus concluded that more individuals are born than can survive so they compete for foodsheltersurvival Darwin39s Four Postulates 0 Four postulates I Individuals in a population vary in traits they possess I Trait differences are heritable I More offspring produced than can survive those that survive produce more offspring I Parents of offspring have certain advantageous traits 0 Outcome of natural selection a change in allele frequency in a population over time o Definition Heritable variation leads to differential reproductive success The Biological Definitions of Fitness Adaptation and Selection I Biological fitness ability of the individual to produce surviving fertile offspring relative to others in the population measure of quantity I Biological adaptation heritable trait that increases fitness of an individual in a particular environment relative to individuals lacking the trait I Opposite of adaptation neutral trait eg hair color Chapter 254 Evolution in Action Recent Research on Natural Selection Case Study 1 How did Mycobacterium tuberculosis become resistant to antibiotics 0 TB infects the lungs and causes fever coughing sweats weight loss death 0 Advances in nutrition and antibiotics decreased importance of TB 0 In 1993 WHO declared TB as a global health emergency drug resistant A Patient History I Admitted with active TB infection I Given antibiotics for six weeks followed by twice weeky doses of rifampin for 33 additional weeks I Ten months of therapy culture showed no TB I Two months later patient readmitted w active TB resistance to antibiotics including rifampin death due to respiratory failure ten days later I Examination of M tuberculosis DNA showed a print mutation in a gene called rpoB A Mutation in a Bacterial Gene Confers Resistance I rpoB codes for a component of RNA polymerase which transcribes DNA to mRNA I Cytosine changed to thymine amino acid serine changed to leucine I Change of protein shape antibiotic can39t bind I Few bacteria w mutation rifampin kills normal bacteria mutated bacteria reproduce Biology 180 Page 1 new population resist to drug Testing Darwin39s Postulates I Was the trait heritable III rpoB is passed onto offspring III phenotype due to genotype I Was there variation in reproductive success III small number of bacteria survived first round of antibiotics I Did selection occur III in presence of antibiotics mutated bacteria selected I Natural selection acts on individuals but populations evolve Case Study 2 Why Are Beak Size Beak Shape and Body Size Changing in Galapagos Finches 0 Peter and Rosemary Grant study finches on Daphne Major in the Galapagos Selection during Drought Conditions I 1977 drought 84 finches disappeared I Natural experiment compare treatment groups by unplanned change in environment I Survivors tended to have deep beaks Continued Changes in Environment Continued Selection Continued Evolution I 1983 heavy rain sma beaked finches reproduced rapidly Why Genes Are Under Selection I Polygenic difficult to identify I Clifford Tabin s lab studies beak development by looking at variation in cell expression of cellcell signals important to development of chicken beaks I In situ hybridization showed where cellcell signal gene called Bmp4 is expressed I Strong correlation between amount of Bmp4 expressed and the widthdepth of adult beak I Suggests that alleles for molecule called calmodulin involved in calcium signaling affects beak length Biology 180 Page 2
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