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LECTURE 8 EVOLUTION IN ACTION Galapagos Finches – • Darwin believed it was “descent with modification” from a common ancestor or evolution  more finches on island than mainland; diversity matching diverse food source; mainland moved to island; large differences in sizes Beaks of Darwin’s Finches • In 1973, Peter and Rosemary Grant embarked on a study of the medium ground finch – Geospiza fortis feeds preferentially on small tender seeds abundantly available in wet years – birds resort to larger, harder seeds in dry years • The Grants found out that the beak depth changed predictably year after year  Wanted to see if evolution happen over short period of time, natural selection do over millions of years.  after drought (large seeds) survivors bill longer and (wet year) shorter  Env selective pressure on species; Natural Selection Causes Evolution • Survival and reproduction are not random. Current research supports Darwin’s hypothesis (small beak more common) Distribution of Peppered Moth forms in the United Kingdom H.B.D. (Bernard) Kettlew ell Evolution by Pollution Evolution of industrial melanism in the peppered moth Peppered Moths and Industrial Melanism • Before 1850 dark moths rare • Industrial pollution: blackened trees • Black moths favored: more difficult to see by bird predators • Result: black variant replaces white in polluted areas Conclusion:  natural selection caused evolution collect dark rare moth, but became common since replaced to better camouflage • Natural selection Concealment hypothesis Natural Selection Explains Descent With Modification 1. Individuals in a population have variable traits that are heritable (eg. color) 2. Predators eat the moths that are easier to spot environment best fit 3. Individuals that survive and reproduce are not a random sample of the population - Essence of evolution by natural selection: heritable variation leads to differential survivaland reproduction Evolution of Heavy Metal Tolerance in Plants • tolerant genotypes invade mine tailings • gene flow between field and mine often restricted because of evolution of physiological and reproductive isolating mechanisms (mutation to tolerate metal) – variation present in population before open mine towards soil env dictates which offspring tolerant as result of pollution Evolution in Agriculture HERBICIDE RESISTANCE • herbicides kill weeds (definition compete with crop) • sprays drift from cultivated land • How does resistance occur?  variation in population; variation to survive and tolerate herbicide and reproduce and pass on trait RESISTANCE IN INSECTS • crops sprayed with insecticide • some insects are resistant to insecticide…why? Natural variation present in population; variation present but those survived offspring has resistance gene • resistance passed on to offspring Return of an Ancient Killer • Tuberculosis has infected humans for 1000s of years caused by bacteria – Evidence of TB has been found in Egyptian mummies – In 1906, TB accounted for 2 out of every 1000 deaths in the U.S. • Transmission of TB occurs through the air, from infected individuals – A single sneeze can contain 40,000 droplets, all containing infectious bacteria(microorganisms) Return of an Ancient Killer -Tuberculosis • Symptoms of TB include: – cough that produces blood – fever – fatigue – period of wasting – patient becomes weaker and thinner • led to calling the disease “consumption” 19 and early 20 century – treatment consisted of “sanitariums”  separate people so cant infect How Did Mycobacterium tuberculosis Become Resistant to Antibiotics? • Mycobacterium tuberculosis causes tuberculosis (TB) • 1950-1990: sanitation, nutrition helped reduce deaths • discovery of antibiotics revolutionized TB treatment • since the 1980s, scientists have noticed an increase in TB that is resistant to antibiotics • TB is on the rise again Case History • patient with TB was treated with antibiotics for 33 weeks; considered cured • 2 mo later, TB had returned and man died WHY?  Some bacteria survived and was in small number so undiscoverable but resistant Alleles That Confer Drug Resistance 1. Large population of M. tuberculosis bacteria in patient’s lungs makes him sick. 2. Drug therapy begins killing most M. tuberculosis. Patient seems cured and drug therapy is ended. However, a few of the original bacteria had a point mutation that made them resistant to the drug treatment. 3. The mutant cells proliferate, resulting in another major infection of the lungs. The patient becomes sick again. 4. A second round of drug therapy begins but is ineffective on the drug resistant bacteria. The patient dies. - Result: drug resistance: mutant cells grow in presence of drug DNA and RNA • DNA 4 bases: guanine (G), cytosine (C), adenine (A), thymine (T) • RNA 4 bases: G, C, A, and uracil (U) (replaces T) • DNA and the Genetic Code Serine replaced by leucine  one base mutation • Mutations and Drug Resistance • DNA from the antibiotic resistant bacteria that killed had a single mutation (C-T mutation = cytosine replaced by thymine) Result: in C-T mutation, serine changed to leucine: prevents rifampin drug from binding to enzyme of bacteria and bacteria continues reproducing substituted for another to resist enzyme from transcribe DNA to RNA Natural Selection Result: •cells with the mutant gene now had a huge selective advantage Environment with no antibiotics – non-mutant cells survive better Environment with antibiotics – resistant mutants survive better and reproduce Natural selection caused evolution—a change in genetic structure over time Mycobacterium tuberculosis • Did variation exist in the population?  in terburculosis - YES • Was variation heritable? YES passed on to offspring • Was there variation in reproductive success between the 2 strains?  YES – after antibiotic was resistant work well • Did selection occur? YES Natural Selection and Human Health - TuberculosisFits Darwin’s Observations • Mycobacterium tuberculosis has evolved resistance to antibiotics: it fulfills the same observations Darwin made 1. bacteria in th
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