Lecture 8 BIO 311D 2nd Edition Outline of Last Lecture I Microevolution occurs when H W equilibrium assumptions are not met II The process of evolution by natural selection Outline of Current Lecture I Multiple selection factors working at once including heterozygote advantage II Evolution occurs in populations over time Current Lecture I Multiple selection factors working at once including heterozygote advantage A 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 time B 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 clover plant 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 sex II D 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 Evolution occurs in populations over time A Micro change in allele frequency within a species Macro evolution above the species level new species form B Review Questions 1 Evolution is a theory about the origin of life on earth False about changes in organisms over time 2 Individual organisms cannot evolve during a single lifespan True 3 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 environment 5 Evolution only occurs slowly and gradually False can occur rapidly 6 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 finches Every 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 or dry 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 life
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