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Examples of Evolution by Natural Selection Microevolution vs. Macroevolution Microevolution is intraspecific evolution, evolution WITHIN a species. Macroevolution is speciation. One species evolves into a new species. Examples of Evolution by Natural Selection Example #1: Antibiotic Resistance This is a famous example, known by almost everyone but rarely called “evolution.” But it is !!! We hear “resistance develops” or resistance emerges” etc. In fact, resistance evolves.* AR is a fine example of very fast evolution AND A fine example of one way Darwinian evolution is important to your health and well-being. *They DO NOT “become immune to the antibiotics.” This phenomenon is NOTHING like you getting a flu shot!! Examples of Evolution by Natural Selection Example #1: Antibiotic Resistance AR is the “poster-child” for rapid evolution.* If we develop a new antibiotic this year and… a resistant strain of bacteria develops in a London hospital … • • resistant strains will evolve and be in all London hospitals in 6 months and… they will be observed in Hong Kong in two years, i.e. they will have moved around the Earth in two years. How does that happen? *Steven Sterns, Yale U. Examples of Evolution by Natural Selection Example #1: Antibiotic Resistance Examples of Evolution by Natural Selection Example #2: Pesticide Resistance Insecticides, Fungicides, Herbicides Consider DDT, the first widely used synthetic insecticide. (see first page of chapter 13) Examples of Evolution by Natural Selection Example #2: Pesticide Resistance Insecticides, Fungicides, Herbicides Consider DDT, the first widely used synthetic insecticide. Species Resistant to Insecticides • • • • • • 1948: 14 1956: 69 1970: 224 1976: 364 1984: 447 1989: 504 Example #2: Pesticide Resistance Herbicide Resistance in 6 Species of Plants in Czech Republic Examples of Evolution by Natural Selection Example #3: The Peppered Moth Biston betularia Industrial Melanism in a Night-flying Moth The Peppered Moth, Biston betularia an example of directional selection Fig. 18-6a1, p.288 Natural Selection in the Peppered Moth H.B.D. Kettlewell Mark and Recapture Experiments Differential Predation Observations (freshly killed moths placed on trees and watched) (using caged females w/ pheromones) %Recaptured Woodland Melanics Pepper Urban 27.5% 13.0% Rural 6.3% 12.5% This shows a difference but does not prove that birds CAUSED it. Woodland Urban Rural # moths eaten by birds Melanics Pepper 15 43 164 26 Science is “roll up your sleeves” process… HBD doesn’t even wear a shirt !!! ;-) Industrial melanism is seen in more than 70 species of British moths; all show patterns similar to that seen in B. betularia. Evolution by Natural Selection: The Peppered Moth Left: Kettelwell, 1956 Right: Grant et.al. 1998 Grant's comments on these maps: "The maps show a before-after comparison of the geographic distribution of melanic phenotypes in peppered moth populations in Britain based on Kettlewell's 1956 survey (left map) and that conducted 40-years later (1996) by my colleagues and me (right map). The black segments of the pie charts indicate the percentage of melanics at the various locations. Clearly melanism has declined everywhere it was once common." (Grant, personal communication, February 11, 2002) The source publication for these maps: Grant, B. S., Cook, A. D. , Clarke, C. A., and Owen, D. F. 1998. Geographic and temporal variation in the incidence of melanism in peppered moth populations in America and Britain. Journal of Heredity 89:465-471. Examples of Evolution by Natural Selection Example #4: Sickle-cell Anemia and Malaria Example #4: Sickle-cell Anemia and Malaria Okay, let’s simplify it… HbA = “N” = normal HbS = “S” = sickle cell NN = “normal” Ns = “normal but carrier” sN = “normal but carrier” ss = sickle-cell anemia The Genetic Basis of Sickle Cell Anemia HbA vs Hbβ: Everyone has HbA (141), and Hb-non-A (146)” HbS is a mutant form of HbA The Genetic Basis of Sickle Cell Anemia The Distribution of the Sickle-Cell Gene less than 1 in 1,600 1 in 400-1,600 1 in 180-400 1 in 100-180 1 in 64-100 more than 1 in 64 Fig. 18-13b, p.293 Malaria: the Plasmodium parasite Sickle cell anemia is a genetic disease of the blood. Malaria is parasitic disease of the blood. What is the relationship between these two diseases? The Distribution of Falciparum Malaria Fig. 18-13a, p.293 Geographic Distribution of Malaria vs. Sickle-cell Anemia Sickle-Cell Trait: Heterozygote Advantage or heterosis or hybrid vigor Allele HbS causes sickle-cell anemia when homozygous Heterozygotes (NS) are more resistant to malaria than homozygotes (SS or NN) Malaria case Sickle-cell trait less than 1 in 1,600 1 in 400-1,600 1 in 180-400 1 in 100-180 1 in 64-100 more than 1 in 64 What Is Our View of Darwin’s Idea Today? The Modern Synthesis: Darwinism Meets Genetics To his credit, his idea has withstood the scrutiny of about 150 years of scientific testing. But a lot has happened in 150 years. What Is Our View of Darwin’s Idea Today? Neo-Darwinism = The Modern Synthesis Neo-Darwinism @ Darwin + Modern Genetics What Is Our View of Darwin’s Idea Today? Neo-Darwinism = The Modern Synthesis Neo-Darwinism @ Darwin + Modern Genetics What Is Our View of Darwin’s Idea Today? Neo-Darwinism = The Modern Synthesis Neo-Darwinism @ Darwin + Modern Genetics What Is Our View of Darwin’s Idea Today? Neo-Darwinism = The Modern Synthesis Neo-Darwinism @ Darwin + Modern Genetics What Is Our View of Darwin’s Idea Today? Neo-Darwinism = The Modern Synthesis Neo-Darwinism @ Darwin + Modern Genetics What Is Our View of Darwin’s Idea Today? Neo-Darwinism = The Modern Synthesis Neo-Darwinism @ Darwin + Modern Genetics And also every other branch of biology that has grown since 1859 and contributes to our understanding of Darwin’s idea, i.e. all of them. Especially... All the “Comparatives” Comparative Anatomy (morphology) Comparative Embryology (development) Comparative Ethology (behavior) Comparative Biochemistry (molecular biology: proteins and DNA) Biogeography (where do they live and why?) Paleontology (the fossil record) Vestigial Structures (the “scars” of evolution) Neo-Darwinism = The Modern Synthesis evidence from Comparative Anatomy (morphology) Comparative Anatomy homologous structures (vs analogous structures) Human Cat Bat Whale Figure 13.8 Comparative Anatomy homologous structures (vs analogous structures) Human Cat Bat Whale Figure 13.8 Comparative Embryology Neo-Darwinism = The Modern Synthesis evidence from Comparative Embryology (development) Comparative Embryology Pharyngeal pouches Post-anal tail Chicken embryo Human embryo Figure 13.9 Neo-Darwinism = The Modern Synthesis evidence from Molecular Biology (Comparative Biochemistry) Neo-Darwinism = The Modern Synthesis evidence from Comparative Biochemistry (= comparative molecular biology) What mutation could cause isoleucine (Ile) to change to phenylalanine (Phe)? And what mutation can change Leucine (Leu) to Arginine (Arg) Primate Percent of selected DNA sequences that match a chimpanzee’s DNA 92% 96% Chimpanzee Human Gorilla Orangutan Gibbon Old World monkey Figure 13.10 100% Neo-Darwinism = The Modern Synthesis evidence from Comparative Biochemistry We can calculate rates of mutation particularly in very stable genes or pseudogenes and use them as clocks Cytochrome C: yeast, wheat, human Neo-Darwinism = The Modern Synthesis evidence from Biogeography Cenozoic Present Eurasia 65 Africa South America India Madagascar Antarctica Paleozoic 251 million years ago Mesozoic 135 Laurasia Figure 14.17 Neo-Darwinism = The Modern Synthesis evidence from Paleontology (fossils) Neo-Darwinism = The Modern Synthesis evidence from Paleontology: The Fossil Record Fossil Record Neo-Darwinism = The Modern Synthesis evidence from Vestigial Structures The Recurrent Laryngeal Nerve vestiges, the “scars” of evolution The Recurrent Laryngeal Nerve vestiges, the “scars” of evolution Neo-Darwinism = The Modern Synthesis evidence from Vestigial Structures Neo-Darwinism = The Modern Synthesis evidence from Vestigial Structures Does Evolution occur by mechanisms other than natural selection? YES. Evolution can… be slow or fast; and it can be helpful, harmful or neutral. Does Evolution occur by mechanisms other than natural selection? OK, how about this question… Does Evolution not occur? What’s necessary for equilibrium? NO mutation NO gene flow NO genetic drift NO nonrandom mating (i.e. totally random mating) NO natural selection A large population. ALL OF THESE CONDITIONS OCCURRING SIMULTANEOUSLY IS UNLIKELY! Analyzing Gene Pools The gene pool is a reservoir from which the next generation draws its genes. Alleles in a gene pool occur in certain frequencies. When thinking about evolution, think gene pool ! Evolution is a change in the genetic make-up of a POPULATION (gene pool) Does Evolution occur by mechanisms other than natural selection? The 3 main causes of evolutionary change are: • Genetic drift • Gene flow • Natural selection (only natural selection is adaptive) Does Evolution occur by mechanisms other than natural selection? Let’s look at Genetic Drift. Just consider the two words: Natural Selection vs. Genetic Drift Genetic Drift Genetic drift is: • A change in the gene pool of a small population • Due to chance events. • Compare the words: “drift” vs “selection.” Genetic Drift e.g. Founder Effect and Bottleneck Effect Genetic Drift Oreaster reticularum in Bahamas… Non-random mating Examples from textbook… Non-random mating (small population of flowers) Bottleneck Effect (cheetahs) Founder Effect (humans on Tristan da Cahuna) The Caribbean Cushion Star • A change in the gene pool of a small population • Due to chance Flower Example from Text Figure 13.19 Genetic Drift is: A change in the gene pool of a small population, …due to chance rr RR RR Only 5 of 10 plants leave offspring Rr rr Rr Rr Rr RR Rr Generation 1 p (frequency of R)) 0.7 q (frequency of (r) 0.3 RR rr RR RR rr Rr RR Only 2 of 10 plants leave offspring RR RR RR RR RR RR RR RR RR Rr Rr Generation \22 RR Generation 3 p 0.5 q 0.5 p 1.0 q 0.0 Figure 13.22-3 RR The Bottleneck Effect The bottleneck effect: • Is an example of genetic drift • Results from a drastic reduction in population size often due to some catastrophic event. Original population Bottlenecking event Surviving population The Bottleneck Effect The bottleneck effect: • Is an example of genetic drift • Results from a drastic reduction in population size • The hunting of large cats like the cheetah Bottlenecking in a population usually reduces genetic variation because at least some alleles are likely to be lost from the gene pool. Cheetahs appear to have experienced at least two genetic bottlenecks in the past 10,000 years. The Founder Effect The founder effect is likely when a few individuals colonize an isolated habitat and represent genetic drift in a new colony. The founder effect explains the relatively high frequency of certain inherited disorders among some small human populations. • Huntington’s Disease around Lake Maracaibo Venezuela • Hereditary blindness on Tristan da Cuhana • Galapagos species (drift + selection) Founder Effect Africa South America Tristan da Cunha Figure 13.25 Gene Flow Gene flow: • Is genetic exchange with another population • Tends to reduce genetic differences between populations Three General Outcomes of Natural Selection Directional selection: • Shifts the phenotypic “curve” of a population • Selects in favor of some extreme phenotype Disruptive selection: • can lead to a balance between two or more contrasting phenotypic forms in a population. Stabilizing selection: • Favors intermediate phenotypes • Is the most common Frequency of individuals Original population Phenotypes (fur color) Original population Evolved population (a) Directional selection (b) Disruptive selection (c) Stabilizing selection Sexual Selection Sexual dimorphism is: • A distinction in appearance between males and females • Not directly associated with reproduction or survival Sexual selection is a form of natural selection in which inherited characteristics determine mating preferences. (a) Sexual dimorphism in a finch species (b) Competing for mates Figure 13.29 (a) Sexual dimorphism in a finch species Figure 13.29a (b) Competing for mates Figure 13.29b Population Genetics and Health Science The Hardy-Weinberg formula can be used to calculate the percentage of a human population that carries the allele for a particular inherited disease. Go over this in book on your own. END OF CHAP 13 ON TO CHAP 14 Old slides PKU: • Is a recessive allele that prevents the breakdown of the amino acid phenylalanine • Occurs in about one out of every 10,000 babies born in the United States INGREDIENTS: SORBITOL, MAGNESIUM STEARATE, ARTIFICIAL FLAVOR ASPARTAME† (SWEETENER), INGREDIENTS: SORBITOL, MAGNESIUM STEARATE, ARTIFICIAL FLAVOR † PHENYLKETONURICS: CONTAINS PHENYLALANINE The Hardy-Weinberg formula can be used to calculate the frequencies of genotypes in a gene pool from the frequencies of alleles. (p+q)2 = p2 + 2pq + q2 = 1 Let’s do a simple analysis of a gene pool: Set these conditions: Just one trait, (let’s say fur color) With just two alleles, B + r And one dominant (B) and the other recessive (r) Let’s say the genes exist the in the gene pool at 50-50. The Hardy-Weinberg formula can be used to calculate the frequencies of genotypes in a gene pool from the frequencies of alleles. (p+q)2 = p2 + 2pq + q2 = 1 (B+r)2 = B2 + 2Br + r2 = 1 So, p = B = black, the dominant gene And q = r = red the recessive gene Shuffle up and deal… Hardy Weinberg What is YOUR genotype? What is YOUR phenotype? What alleles do YOU have? What is the population’s gene frequencies for B? for r? Hardy-Weinberg Equilibrium OK, mate (randomly). Give a gamete to anyone else until everyone has two. Has anything changed in the gene pool? Has anything changed? Has the population evolved? Genotype frequencies: • Can be calculated from allele frequencies • Are symbolized by the expressions p2, 2pq, and q2 To refresh our memories, consider the more complex but familiar multiple-allele Human ABO Blood Types… Neither A nor B is dominant to the other, o is recessive. A, B, O are the three alleles AA, Ao, BB, Bo, AB, oo are the six genotypes Type A, Type B, Type AB and Type O are the four phenotypes.