Lecture 8 BIO 311D 2nd EditionOutline of Last Lecture I. Microevolution occurs when H-W equilibrium assumptions are not metII. The process of evolution by natural selectionOutline of Current Lecture I. Multiple selection factors working at once, including heterozygote advantageII. Evolution occurs in populations over timeCurrent LectureI. Multiple selection factors working at once, including heterozygote advantageA. Natural Selection- Operates on individuals (according to their phenotypes), not on alleles- The pattern of evolution by natural selection depends upon the particular environment at the timeB. Example- An evolutionary change in the peppered moth occurred in English cities with heavy industry.Over the course of 40 years, the normal speckled variety was almost entirely replaced by a much darker “melanized” variety that was better camouflaged on sooty bark. Then in 1956, the U.K. passed a Clean Air Act that greatly reduced pollution and led to a gradual disappearance of environmental soot. The prevalence of melanized moths has steadily declined in subsequent years. - Geographic variation in cyanide (HCN)- producing clover plants HCN is a good defense mechanism against predators because once they try eating the cloverplant; the HCN is released giving it a very bitter taste. However, clover plants with HCN are more prevalent in warmer areas compared to colder areas. In cold climates, the plant cells freeze, membranes become damaged, and as the plant thaws the HCN is released harming the plant itself.- Long term studies of Trinidad guppies and their predators, living in many different pools along the Aripo River. Investigators saw evolution of male color patterns depending on type of predators present.C. Sexual Selection- Some sex-specific traits are the result of sexual selection (fitness differences resulting from preferences of certain traits by the opposite sex)- Mate choice- Interaction of individuals of the same sexD. Heterozygote advantage- Sickle- cell allele: frequency of the allele is high in certain parts of Africa because in environments with malaria present, heterozygote carriers of the sickle cell trait have greater fitness- If 9% of African population is born with a severe form of sickle-cell anemia (S’S’), what percentage of the population will be more resistant to malaria because they are heterozygous (SS’)? 42% In populations that move away from malaria areas, the frequency of the sickle-cell globin allele would decrease. II. Evolution occurs in populations over timeA. Micro: change in allele frequency within a speciesMacro: evolution above the species level, new species formB. Review Questions 1. Evolution is a theory about the origin of life on earth False; about changes in organisms over time2. Individual organisms cannot evolve during a single lifespan True3. Evolution can occur by means that do not involve any selection True; mutation, gene flow, etc.4. Organisms get better and better, not worse, as they evolve False; they just become more adaptive to “that” certain environment5. Evolution only occurs slowly and gradually False, can occur rapidly6. Natural selection gives organisms what they need False C. Natural selection doesn’t produce “perfect” organisms- Evolution is limited by historical constraints- Adaptations are often compromises, more than one selective factor acting at once- Chance and natural selection both affect the course of evolution D. Examples- Study of the Galapagos ground finchesEvery single finch on a particular small island was individually marked. The nest success, offspring condition, survival, body traits, use of space and food were all measured. Beak size evolved in response to competition as food types present differed in usually wet ordry years. E. Heritability - A quantitative measure of the degree to which a parental trait is passed along the offspring. F. Adaptation - An inherited characteristic of an organism that enhances its survival and reproduction in a specific environment- Galapagos Finches Macroevolution was a result of adaptive radiation. Adaptive radiation is the emergence of numerous species from a common ancestor, each species adapted to a slightly different environment or way of
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