Examples of Evolution by Natural Selection

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.

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!!

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.

Example #1: Antibiotic Resistance

Example #2: Pesticide Resistance Insecticides, Fungicides, Herbicides (see first page of chapter 13) Consider DDT, the first widely used synthetic insecticide.

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

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 Differential Predation Observations (freshly killed moths placed on trees and watched) # moths eaten by birds Woodland Melanics Pepper Urban 15 43 Rural 164 26 Mark and Recapture Experiments (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. 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 Geographic and temporal variation in the incidence of melanism in peppered moth populations in America and Britain. Journal of Heredity 89:

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 1 in 1 in more than 1 in 64 Fig b, 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 a, 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 1 in 1 in more than 1 in 64

What Is Our View of Darwin’s Idea Today
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 Darwin + Modern Genetics

What Is Our View of Darwin’s Idea Today? Neo-Darwinism = The Modern Synthesis 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)
Figure 13.8 Homologous structures: anatomical signs of descent with modification Human Whale Bat Cat Figure 13.8

Comparative Embryology

Neo-Darwinism = The Modern Synthesis evidence from Comparative Embryology (development)

Comparative Embryology
Pharyngeal pouches Post-anal tail Figure 13.9 Evolutionary signs from comparative embryology Chicken embryo Human embryo Figure 13.9

Neo-Darwinism = The Modern Synthesis evidence from Molecular Biology (Comparative Biochemistry)

And what mutation can change Leucine (Leu) to Arginine (Arg)
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)

Percent of selected DNA sequences that match a chimpanzee’s DNA
Primate Percent of selected DNA sequences that match a chimpanzee’s DNA 92% 96% 100% Chimpanzee Human Gorilla Orangutan Figure Genetic relationships among some primates Gibbon Old World monkey Figure 13.10

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

Figure 14.17 Present Cenozoic 65 135 Mesozoic 251 million years ago
North America Eurasia 65 Africa South America India Madagascar Australia Antarctica Laurasia 135 Mesozoic Gondwana Figure The history of plate tectonics 251 million years ago Pangaea Paleozoic 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

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.

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 ! Student Misconceptions and Concerns 1. Students may suggest that individuals evolve. As this chapter section clarifies, populations are the smallest units that can evolve. Individuals cannot have diversity from which to select. However, individuals can change during their lifetime in response to activities. Muscles can grow stronger because of use. However, these individual changes are not passed on to the next generation (after all, boys have been circumcised for thousands of years but are still born with a foreskin). 2. Another misperception is that evolution results from need. Challenge your students to explain how need and want have nothing to do with evolution (because neither need nor want can generate genetic variation!) 3. Students may think of mutations in a positive sense, as if they come as needed. Yet, mutations in key genes are the cause of cancer and other diseases. Only rarely does a mutation lead to a change that increases the chances for survival. However, these rare events can become significant if given enough time. (As the authors note: A random mutation is like a shot in the dark; it is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance.) Teaching Tips 1. It might be interesting to discuss with students whether the Internet would have helped Mendel and Darwin. Is the Internet facilitating scientific communication? Has this technology created new problems in the process? 2. Try to find good, local examples of populations. If you live near a seashore, the many invertebrate populations (starfish, sea urchin, and kelp) would be great. Further inland we find somewhat isolated populations of fish and continuous and clumped populations of squirrels, separated by vast fields of corn, wheat, or soybeans! Bring the subject home with local examples. 3. No doubt about it, the Hardy-Weinberg equation is problematic for some students. Students should create a quick reference key to the definitions of the elements. Consider some practice problems varying the value of p and q. 4. Heterozygotes can form in two ways, the recessive from mom, the dominant from dad...or the reverse. This should serve to remind students that the 2pq portion of the equation represents the heterozygotes. 5. Another example that can be used for Hardy-Weinberg practice is cystic fibrosis. Cystic fibrosis strikes about one out of every 3300 Caucasian children. It results from the homozygous recessive condition. Thus, q2 would equal 1/3300 = and q = the square root of = The frequency of carriers = 2pq = 2 x x = = 3.42%, about one in every 29 Caucasian adults. To bring the point home to your class, divide the number of Caucasian students in your class by 29 to estimate the number of students who are carriers. (Source of information is: Fertil. Steril Jan 85(1): ) Evolution is a change in the genetic make-up of a POPULATION (gene pool)

The 3 main causes of evolutionary change are: Genetic drift Gene flow Natural selection (only natural selection is adaptive)

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.” Student Misconceptions and Concerns 1. The concept of a genetic bottleneck contributing to a loss of diversity can be difficult for some students to understand. Without an appreciation for population genetics, students might think that a recovery in sheer numbers of individuals is all that is needed. Yet, the loss of genetic diversity might doom a population eventually faced with widespread disease. 2. Sampling error can be difficult for some students to immediately understand. Have students work in pairs to flip a coin 10 times. For each pair, list the number of heads on the board as just a long list of numbers (no need to keep track of heads and tails). This can be done quickly as long as you have been sure to bring enough pennies. Now analyze the results. There should be considerable variation from the expected five. Now determine the average of all the groups, and the collective sample size. By pooling the results, and increasing the sample size, the means should be closer to five. Teaching Tips 1. The loss of genetic diversity in a population because of the bottleneck effect is a significant problem in conservation. When a species is reduced to relatively few individuals, and then is brought back to abundance by extraordinary efforts, the species is not fully recovered. The lost genetic diversity may be a prerequisite for the long-term survival of the species. Consider challenging your students to identify modern endangered species that might suffer from a genetic bottleneck despite increasing numbers. 2. Students might best relate to the bias of the founder effect by this example. Just for the sake of explanation, consider that you and all the students present in today’s class are the only survivors of some global catastrophe. Would your class adequately represent the biological diversity of the current human population? 3. Challenge your students to explain why evolution primarily addresses only organisms that reproduce. Like people who vote, reproduction contributes to change. Moreover, like non-voters who influence opinions of voters, non-reproducing organisms can still influence the actions of those who do reproduce. Challenge your students to suggest how organisms that do not reproduce might influence the evolution of a species. (One such example is the benefit of a sibling helping to raise its nieces / nephews.) 4. Students are often surprised to learn that overweight human newborns can be as unhealthy as underweight newborns. Thus, stabilizing selection favors human birth weights clustered narrowly around a mean weight. 5. Consider challenging your students to distinguish between natural selection generally, sexual selection specifically, and artificial selection. One criterion for comparison is the nature of the selective environment. In natural selection, the interaction is between the organism and its immediate environment. In sexual selection, competition occurs within a species for access to mates. In artificial selection, humans act as the environment, favoring traits of human interest. 6. At the conclusion of this chapter information, it might be a good time to remind your students that most species that have ever lived are now extinct. Species do not have a mechanism to get what they need to survive. The natural variation inherited from the immediate ancestors and the new variations that emerge from mutations and genetic combinations are the raw materials for survival. No amount of need can influence the variety upon which selection must act. It is, therefore, quite possible that the variety in any generation is insufficient for survival. Periods of relatively fast environmental change may require traits insufficient for survival.

Genetic Drift e.g. Founder Effect and Bottleneck Effect

Genetic Drift Oreaster reticularum in Bahamas… Examples from textbook…
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 A population of wildflowers with two varieties of color. Figure 13.19

Genetic Drift is: A change in the gene pool of a small population, …due to chance
RR rr RR RR RR Only 5 of 10 plants leave offspring Only 2 of 10 plants leave offspring RR Rr Rr RR RR rr RR rr RR RR Rr Rr RR RR RR RR Rr rr RR Rr RR Figure Genetic drift (Step 3) Rr Rr RR RR Generation 3 Generation 1 Generation \22 p (frequency of R))  0.7 q (frequency of (r)  0.3 p  0.5 q  0.5 p  1.0 q  0.0 Figure

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. Student Misconceptions and Concerns 1. The concept of a genetic bottleneck contributing to a loss of diversity can be difficult for some students to understand. Without an appreciation for population genetics, students might think that a recovery in sheer numbers of individuals is all that is needed. Yet, the loss of genetic diversity might doom a population eventually faced with widespread disease. 2. Sampling error can be difficult for some students to immediately understand. Have students work in pairs to flip a coin 10 times. For each pair, list the number of heads on the board as just a long list of numbers (no need to keep track of heads and tails). This can be done quickly as long as you have been sure to bring enough pennies. Now analyze the results. There should be considerable variation from the expected five. Now determine the average of all the groups, and the collective sample size. By pooling the results, and increasing the sample size, the means should be closer to five. Teaching Tips 1. The loss of genetic diversity in a population because of the bottleneck effect is a significant problem in conservation. When a species is reduced to relatively few individuals, and then is brought back to abundance by extraordinary efforts, the species is not fully recovered. The lost genetic diversity may be a prerequisite for the long-term survival of the species. Consider challenging your students to identify modern endangered species that might suffer from a genetic bottleneck despite increasing numbers. 2. Students might best relate to the bias of the founder effect by this example. Just for the sake of explanation, consider that you and all the students present in today’s class are the only survivors of some global catastrophe. Would your class adequately represent the biological diversity of the current human population? 3. Challenge your students to explain why evolution primarily addresses only organisms that reproduce. Like people who vote, reproduction contributes to change. Moreover, like non-voters who influence opinions of voters, non-reproducing organisms can still influence the actions of those who do reproduce. Challenge your students to suggest how organisms that do not reproduce might influence the evolution of a species. (One such example is the benefit of a sibling helping to raise its nieces / nephews.) 4. Students are often surprised to learn that overweight human newborns can be as unhealthy as underweight newborns. Thus, stabilizing selection favors human birth weights clustered narrowly around a mean weight. 5. Consider challenging your students to distinguish between natural selection generally, sexual selection specifically, and artificial selection. One criterion for comparison is the nature of the selective environment. In natural selection, the interaction is between the organism and its immediate environment. In sexual selection, competition occurs within a species for access to mates. In artificial selection, humans act as the environment, favoring traits of human interest. 6. At the conclusion of this chapter information, it might be a good time to remind your students that most species that have ever lived are now extinct. Species do not have a mechanism to get what they need to survive. The natural variation inherited from the immediate ancestors and the new variations that emerge from mutations and genetic combinations are the raw materials for survival. No amount of need can influence the variety upon which selection must act. It is, therefore, quite possible that the variety in any generation is insufficient for survival. Periods of relatively fast environmental change may require traits insufficient for survival. Original population Surviving population Bottlenecking event

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 Student Misconceptions and Concerns 1. The concept of a genetic bottleneck contributing to a loss of diversity can be difficult for some students to understand. Without an appreciation for population genetics, students might think that a recovery in sheer numbers of individuals is all that is needed. Yet, the loss of genetic diversity might doom a population eventually faced with widespread disease. 2. Sampling error can be difficult for some students to immediately understand. Have students work in pairs to flip a coin 10 times. For each pair, list the number of heads on the board as just a long list of numbers (no need to keep track of heads and tails). This can be done quickly as long as you have been sure to bring enough pennies. Now analyze the results. There should be considerable variation from the expected five. Now determine the average of all the groups, and the collective sample size. By pooling the results, and increasing the sample size, the means should be closer to five. Teaching Tips 1. The loss of genetic diversity in a population because of the bottleneck effect is a significant problem in conservation. When a species is reduced to relatively few individuals, and then is brought back to abundance by extraordinary efforts, the species is not fully recovered. The lost genetic diversity may be a prerequisite for the long-term survival of the species. Consider challenging your students to identify modern endangered species that might suffer from a genetic bottleneck despite increasing numbers. 2. Students might best relate to the bias of the founder effect by this example. Just for the sake of explanation, consider that you and all the students present in today’s class are the only survivors of some global catastrophe. Would your class adequately represent the biological diversity of the current human population? 3. Challenge your students to explain why evolution primarily addresses only organisms that reproduce. Like people who vote, reproduction contributes to change. Moreover, like non-voters who influence opinions of voters, non-reproducing organisms can still influence the actions of those who do reproduce. Challenge your students to suggest how organisms that do not reproduce might influence the evolution of a species. (One such example is the benefit of a sibling helping to raise its nieces / nephews.) 4. Students are often surprised to learn that overweight human newborns can be as unhealthy as underweight newborns. Thus, stabilizing selection favors human birth weights clustered narrowly around a mean weight. 5. Consider challenging your students to distinguish between natural selection generally, sexual selection specifically, and artificial selection. One criterion for comparison is the nature of the selective environment. In natural selection, the interaction is between the organism and its immediate environment. In sexual selection, competition occurs within a species for access to mates. In artificial selection, humans act as the environment, favoring traits of human interest. 6. At the conclusion of this chapter information, it might be a good time to remind your students that most species that have ever lived are now extinct. Species do not have a mechanism to get what they need to survive. The natural variation inherited from the immediate ancestors and the new variations that emerge from mutations and genetic combinations are the raw materials for survival. No amount of need can influence the variety upon which selection must act. It is, therefore, quite possible that the variety in any generation is insufficient for survival. Periods of relatively fast environmental change may require traits insufficient for survival.

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. Student Misconceptions and Concerns 1. The concept of a genetic bottleneck contributing to a loss of diversity can be difficult for some students to understand. Without an appreciation for population genetics, students might think that a recovery in sheer numbers of individuals is all that is needed. Yet, the loss of genetic diversity might doom a population eventually faced with widespread disease. 2. Sampling error can be difficult for some students to immediately understand. Have students work in pairs to flip a coin 10 times. For each pair, list the number of heads on the board as just a long list of numbers (no need to keep track of heads and tails). This can be done quickly as long as you have been sure to bring enough pennies. Now analyze the results. There should be considerable variation from the expected five. Now determine the average of all the groups, and the collective sample size. By pooling the results, and increasing the sample size, the means should be closer to five. Teaching Tips 1. The loss of genetic diversity in a population because of the bottleneck effect is a significant problem in conservation. When a species is reduced to relatively few individuals, and then is brought back to abundance by extraordinary efforts, the species is not fully recovered. The lost genetic diversity may be a prerequisite for the long-term survival of the species. Consider challenging your students to identify modern endangered species that might suffer from a genetic bottleneck despite increasing numbers. 2. Students might best relate to the bias of the founder effect by this example. Just for the sake of explanation, consider that you and all the students present in today’s class are the only survivors of some global catastrophe. Would your class adequately represent the biological diversity of the current human population? 3. Challenge your students to explain why evolution primarily addresses only organisms that reproduce. Like people who vote, reproduction contributes to change. Moreover, like non-voters who influence opinions of voters, non-reproducing organisms can still influence the actions of those who do reproduce. Challenge your students to suggest how organisms that do not reproduce might influence the evolution of a species. (One such example is the benefit of a sibling helping to raise its nieces / nephews.) 4. Students are often surprised to learn that overweight human newborns can be as unhealthy as underweight newborns. Thus, stabilizing selection favors human birth weights clustered narrowly around a mean weight. 5. Consider challenging your students to distinguish between natural selection generally, sexual selection specifically, and artificial selection. One criterion for comparison is the nature of the selective environment. In natural selection, the interaction is between the organism and its immediate environment. In sexual selection, competition occurs within a species for access to mates. In artificial selection, humans act as the environment, favoring traits of human interest. 6. At the conclusion of this chapter information, it might be a good time to remind your students that most species that have ever lived are now extinct. Species do not have a mechanism to get what they need to survive. The natural variation inherited from the immediate ancestors and the new variations that emerge from mutations and genetic combinations are the raw materials for survival. No amount of need can influence the variety upon which selection must act. It is, therefore, quite possible that the variety in any generation is insufficient for survival. Periods of relatively fast environmental change may require traits insufficient for survival.

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) Student Misconceptions and Concerns 1. The concept of a genetic bottleneck contributing to a loss of diversity can be difficult for some students to understand. Without an appreciation for population genetics, students might think that a recovery in sheer numbers of individuals is all that is needed. Yet, the loss of genetic diversity might doom a population eventually faced with widespread disease. 2. Sampling error can be difficult for some students to immediately understand. Have students work in pairs to flip a coin 10 times. For each pair, list the number of heads on the board as just a long list of numbers (no need to keep track of heads and tails). This can be done quickly as long as you have been sure to bring enough pennies. Now analyze the results. There should be considerable variation from the expected five. Now determine the average of all the groups, and the collective sample size. By pooling the results, and increasing the sample size, the means should be closer to five. Teaching Tips 1. The loss of genetic diversity in a population because of the bottleneck effect is a significant problem in conservation. When a species is reduced to relatively few individuals, and then is brought back to abundance by extraordinary efforts, the species is not fully recovered. The lost genetic diversity may be a prerequisite for the long-term survival of the species. Consider challenging your students to identify modern endangered species that might suffer from a genetic bottleneck despite increasing numbers. 2. Students might best relate to the bias of the founder effect by this example. Just for the sake of explanation, consider that you and all the students present in today’s class are the only survivors of some global catastrophe. Would your class adequately represent the biological diversity of the current human population? 3. Challenge your students to explain why evolution primarily addresses only organisms that reproduce. Like people who vote, reproduction contributes to change. Moreover, like non-voters who influence opinions of voters, non-reproducing organisms can still influence the actions of those who do reproduce. Challenge your students to suggest how organisms that do not reproduce might influence the evolution of a species. (One such example is the benefit of a sibling helping to raise its nieces / nephews.) 4. Students are often surprised to learn that overweight human newborns can be as unhealthy as underweight newborns. Thus, stabilizing selection favors human birth weights clustered narrowly around a mean weight. 5. Consider challenging your students to distinguish between natural selection generally, sexual selection specifically, and artificial selection. One criterion for comparison is the nature of the selective environment. In natural selection, the interaction is between the organism and its immediate environment. In sexual selection, competition occurs within a species for access to mates. In artificial selection, humans act as the environment, favoring traits of human interest. 6. At the conclusion of this chapter information, it might be a good time to remind your students that most species that have ever lived are now extinct. Species do not have a mechanism to get what they need to survive. The natural variation inherited from the immediate ancestors and the new variations that emerge from mutations and genetic combinations are the raw materials for survival. No amount of need can influence the variety upon which selection must act. It is, therefore, quite possible that the variety in any generation is insufficient for survival. Periods of relatively fast environmental change may require traits insufficient for survival.

Founder Effect

South America Tristan da Cunha
Africa South America Tristan da Cunha Figure Residents of Tristan daCunha in the early 1900s Figure 13.25

Gene Flow Gene flow: Is genetic exchange with another population
Tends to reduce genetic differences between populations Student Misconceptions and Concerns 1. The concept of a genetic bottleneck contributing to a loss of diversity can be difficult for some students to understand. Without an appreciation for population genetics, students might think that a recovery in sheer numbers of individuals is all that is needed. Yet, the loss of genetic diversity might doom a population eventually faced with widespread disease. 2. Sampling error can be difficult for some students to immediately understand. Have students work in pairs to flip a coin 10 times. For each pair, list the number of heads on the board as just a long list of numbers (no need to keep track of heads and tails). This can be done quickly as long as you have been sure to bring enough pennies. Now analyze the results. There should be considerable variation from the expected five. Now determine the average of all the groups, and the collective sample size. By pooling the results, and increasing the sample size, the means should be closer to five. Teaching Tips 1. The loss of genetic diversity in a population because of the bottleneck effect is a significant problem in conservation. When a species is reduced to relatively few individuals, and then is brought back to abundance by extraordinary efforts, the species is not fully recovered. The lost genetic diversity may be a prerequisite for the long-term survival of the species. Consider challenging your students to identify modern endangered species that might suffer from a genetic bottleneck despite increasing numbers. 2. Students might best relate to the bias of the founder effect by this example. Just for the sake of explanation, consider that you and all the students present in today’s class are the only survivors of some global catastrophe. Would your class adequately represent the biological diversity of the current human population? 3. Challenge your students to explain why evolution primarily addresses only organisms that reproduce. Like people who vote, reproduction contributes to change. Moreover, like non-voters who influence opinions of voters, non-reproducing organisms can still influence the actions of those who do reproduce. Challenge your students to suggest how organisms that do not reproduce might influence the evolution of a species. (One such example is the benefit of a sibling helping to raise its nieces / nephews.) 4. Students are often surprised to learn that overweight human newborns can be as unhealthy as underweight newborns. Thus, stabilizing selection favors human birth weights clustered narrowly around a mean weight. 5. Consider challenging your students to distinguish between natural selection generally, sexual selection specifically, and artificial selection. One criterion for comparison is the nature of the selective environment. In natural selection, the interaction is between the organism and its immediate environment. In sexual selection, competition occurs within a species for access to mates. In artificial selection, humans act as the environment, favoring traits of human interest. 6. At the conclusion of this chapter information, it might be a good time to remind your students that most species that have ever lived are now extinct. Species do not have a mechanism to get what they need to survive. The natural variation inherited from the immediate ancestors and the new variations that emerge from mutations and genetic combinations are the raw materials for survival. No amount of need can influence the variety upon which selection must act. It is, therefore, quite possible that the variety in any generation is insufficient for survival. Periods of relatively fast environmental change may require traits insufficient for survival.

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 Student Misconceptions and Concerns 1. The concept of a genetic bottleneck contributing to a loss of diversity can be difficult for some students to understand. Without an appreciation for population genetics, students might think that a recovery in sheer numbers of individuals is all that is needed. Yet, the loss of genetic diversity might doom a population eventually faced with widespread disease. 2. Sampling error can be difficult for some students to immediately understand. Have students work in pairs to flip a coin 10 times. For each pair, list the number of heads on the board as just a long list of numbers (no need to keep track of heads and tails). This can be done quickly as long as you have been sure to bring enough pennies. Now analyze the results. There should be considerable variation from the expected five. Now determine the average of all the groups, and the collective sample size. By pooling the results, and increasing the sample size, the means should be closer to five. Teaching Tips 1. The loss of genetic diversity in a population because of the bottleneck effect is a significant problem in conservation. When a species is reduced to relatively few individuals, and then is brought back to abundance by extraordinary efforts, the species is not fully recovered. The lost genetic diversity may be a prerequisite for the long-term survival of the species. Consider challenging your students to identify modern endangered species that might suffer from a genetic bottleneck despite increasing numbers. 2. Students might best relate to the bias of the founder effect by this example. Just for the sake of explanation, consider that you and all the students present in today’s class are the only survivors of some global catastrophe. Would your class adequately represent the biological diversity of the current human population? 3. Challenge your students to explain why evolution primarily addresses only organisms that reproduce. Like people who vote, reproduction contributes to change. Moreover, like non-voters who influence opinions of voters, non-reproducing organisms can still influence the actions of those who do reproduce. Challenge your students to suggest how organisms that do not reproduce might influence the evolution of a species. (One such example is the benefit of a sibling helping to raise its nieces / nephews.) 4. Students are often surprised to learn that overweight human newborns can be as unhealthy as underweight newborns. Thus, stabilizing selection favors human birth weights clustered narrowly around a mean weight. 5. Consider challenging your students to distinguish between natural selection generally, sexual selection specifically, and artificial selection. One criterion for comparison is the nature of the selective environment. In natural selection, the interaction is between the organism and its immediate environment. In sexual selection, competition occurs within a species for access to mates. In artificial selection, humans act as the environment, favoring traits of human interest. 6. At the conclusion of this chapter information, it might be a good time to remind your students that most species that have ever lived are now extinct. Species do not have a mechanism to get what they need to survive. The natural variation inherited from the immediate ancestors and the new variations that emerge from mutations and genetic combinations are the raw materials for survival. No amount of need can influence the variety upon which selection must act. It is, therefore, quite possible that the variety in any generation is insufficient for survival. Periods of relatively fast environmental change may require traits insufficient for survival.

Phenotypes (fur color)
of individuals Frequency Original population Phenotypes (fur color) Original population Evolved population Figure Three general effects of natural selection on a phenotypic character (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 Student Misconceptions and Concerns 1. The concept of a genetic bottleneck contributing to a loss of diversity can be difficult for some students to understand. Without an appreciation for population genetics, students might think that a recovery in sheer numbers of individuals is all that is needed. Yet, the loss of genetic diversity might doom a population eventually faced with widespread disease. 2. Sampling error can be difficult for some students to immediately understand. Have students work in pairs to flip a coin 10 times. For each pair, list the number of heads on the board as just a long list of numbers (no need to keep track of heads and tails). This can be done quickly as long as you have been sure to bring enough pennies. Now analyze the results. There should be considerable variation from the expected five. Now determine the average of all the groups, and the collective sample size. By pooling the results, and increasing the sample size, the means should be closer to five. Teaching Tips 1. The loss of genetic diversity in a population because of the bottleneck effect is a significant problem in conservation. When a species is reduced to relatively few individuals, and then is brought back to abundance by extraordinary efforts, the species is not fully recovered. The lost genetic diversity may be a prerequisite for the long-term survival of the species. Consider challenging your students to identify modern endangered species that might suffer from a genetic bottleneck despite increasing numbers. 2. Students might best relate to the bias of the founder effect by this example. Just for the sake of explanation, consider that you and all the students present in today’s class are the only survivors of some global catastrophe. Would your class adequately represent the biological diversity of the current human population? 3. Challenge your students to explain why evolution primarily addresses only organisms that reproduce. Like people who vote, reproduction contributes to change. Moreover, like non-voters who influence opinions of voters, non-reproducing organisms can still influence the actions of those who do reproduce. Challenge your students to suggest how organisms that do not reproduce might influence the evolution of a species. (One such example is the benefit of a sibling helping to raise its nieces / nephews.) 4. Students are often surprised to learn that overweight human newborns can be as unhealthy as underweight newborns. Thus, stabilizing selection favors human birth weights clustered narrowly around a mean weight. 5. Consider challenging your students to distinguish between natural selection generally, sexual selection specifically, and artificial selection. One criterion for comparison is the nature of the selective environment. In natural selection, the interaction is between the organism and its immediate environment. In sexual selection, competition occurs within a species for access to mates. In artificial selection, humans act as the environment, favoring traits of human interest. 6. At the conclusion of this chapter information, it might be a good time to remind your students that most species that have ever lived are now extinct. Species do not have a mechanism to get what they need to survive. The natural variation inherited from the immediate ancestors and the new variations that emerge from mutations and genetic combinations are the raw materials for survival. No amount of need can influence the variety upon which selection must act. It is, therefore, quite possible that the variety in any generation is insufficient for survival. Periods of relatively fast environmental change may require traits insufficient for survival.

Sexual selection is a form of natural selection in which inherited characteristics determine mating preferences. Student Misconceptions and Concerns 1. The concept of a genetic bottleneck contributing to a loss of diversity can be difficult for some students to understand. Without an appreciation for population genetics, students might think that a recovery in sheer numbers of individuals is all that is needed. Yet, the loss of genetic diversity might doom a population eventually faced with widespread disease. 2. Sampling error can be difficult for some students to immediately understand. Have students work in pairs to flip a coin 10 times. For each pair, list the number of heads on the board as just a long list of numbers (no need to keep track of heads and tails). This can be done quickly as long as you have been sure to bring enough pennies. Now analyze the results. There should be considerable variation from the expected five. Now determine the average of all the groups, and the collective sample size. By pooling the results, and increasing the sample size, the means should be closer to five. Teaching Tips 1. The loss of genetic diversity in a population because of the bottleneck effect is a significant problem in conservation. When a species is reduced to relatively few individuals, and then is brought back to abundance by extraordinary efforts, the species is not fully recovered. The lost genetic diversity may be a prerequisite for the long-term survival of the species. Consider challenging your students to identify modern endangered species that might suffer from a genetic bottleneck despite increasing numbers. 2. Students might best relate to the bias of the founder effect by this example. Just for the sake of explanation, consider that you and all the students present in today’s class are the only survivors of some global catastrophe. Would your class adequately represent the biological diversity of the current human population? 3. Challenge your students to explain why evolution primarily addresses only organisms that reproduce. Like people who vote, reproduction contributes to change. Moreover, like non-voters who influence opinions of voters, non-reproducing organisms can still influence the actions of those who do reproduce. Challenge your students to suggest how organisms that do not reproduce might influence the evolution of a species. (One such example is the benefit of a sibling helping to raise its nieces / nephews.) 4. Students are often surprised to learn that overweight human newborns can be as unhealthy as underweight newborns. Thus, stabilizing selection favors human birth weights clustered narrowly around a mean weight. 5. Consider challenging your students to distinguish between natural selection generally, sexual selection specifically, and artificial selection. One criterion for comparison is the nature of the selective environment. In natural selection, the interaction is between the organism and its immediate environment. In sexual selection, competition occurs within a species for access to mates. In artificial selection, humans act as the environment, favoring traits of human interest. 6. At the conclusion of this chapter information, it might be a good time to remind your students that most species that have ever lived are now extinct. Species do not have a mechanism to get what they need to survive. The natural variation inherited from the immediate ancestors and the new variations that emerge from mutations and genetic combinations are the raw materials for survival. No amount of need can influence the variety upon which selection must act. It is, therefore, quite possible that the variety in any generation is insufficient for survival. Periods of relatively fast environmental change may require traits insufficient for survival.

(a) Sexual dimorphism in a finch species (b) Competing for mates
Figure Sexual dimorphism (a) Sexual dimorphism in a finch species (b) Competing for mates Figure 13.29

(a) Sexual dimorphism in a finch species
Figure 13.29a Sexual dimorphism: finch species (a) Sexual dimorphism in a finch species Figure 13.29a

(b) Competing for mates
Figure 13.29b Sexual dimorphism: competing for mates (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. Student Misconceptions and Concerns 1. Students may suggest that individuals evolve. As this chapter section clarifies, populations are the smallest units that can evolve. Individuals cannot have diversity from which to select. However, individuals can change during their lifetime in response to activities. Muscles can grow stronger because of use. However, these individual changes are not passed on to the next generation (after all, boys have been circumcised for thousands of years but are still born with a foreskin). 2. Another misperception is that evolution results from need. Challenge your students to explain how need and want have nothing to do with evolution (because neither need nor want can generate genetic variation!) 3. Students may think of mutations in a positive sense, as if they come as needed. Yet, mutations in key genes are the cause of cancer and other diseases. Only rarely does a mutation lead to a change that increases the chances for survival. However, these rare events can become significant if given enough time. (As the authors note: A random mutation is like a shot in the dark; it is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance.) Teaching Tips 1. It might be interesting to discuss with students whether the Internet would have helped Mendel and Darwin. Is the Internet facilitating scientific communication? Has this technology created new problems in the process? 2. Try to find good, local examples of populations. If you live near a seashore, the many invertebrate populations (starfish, sea urchin, and kelp) would be great. Further inland we find somewhat isolated populations of fish and continuous and clumped populations of squirrels, separated by vast fields of corn, wheat, or soybeans! Bring the subject home with local examples. 3. No doubt about it, the Hardy-Weinberg equation is problematic for some students. Students should create a quick reference key to the definitions of the elements. Consider some practice problems varying the value of p and q. 4. Heterozygotes can form in two ways, the recessive from mom, the dominant from dad...or the reverse. This should serve to remind students that the 2pq portion of the equation represents the heterozygotes. 5. Another example that can be used for Hardy-Weinberg practice is cystic fibrosis. Cystic fibrosis strikes about one out of every 3300 Caucasian children. It results from the homozygous recessive condition. Thus, q2 would equal 1/3300 = and q = the square root of = The frequency of carriers = 2pq = 2 x x = = 3.42%, about one in every 29 Caucasian adults. To bring the point home to your class, divide the number of Caucasian students in your class by 29 to estimate the number of students who are carriers. (Source of information is: Fertil. Steril Jan 85(1): )

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), Student Misconceptions and Concerns 1. Students may suggest that individuals evolve. As this chapter section clarifies, populations are the smallest units that can evolve. Individuals cannot have diversity from which to select. However, individuals can change during their lifetime in response to activities. Muscles can grow stronger because of use. However, these individual changes are not passed on to the next generation (after all, boys have been circumcised for thousands of years but are still born with a foreskin). 2. Another misperception is that evolution results from need. Challenge your students to explain how need and want have nothing to do with evolution (because neither need nor want can generate genetic variation!) 3. Students may think of mutations in a positive sense, as if they come as needed. Yet, mutations in key genes are the cause of cancer and other diseases. Only rarely does a mutation lead to a change that increases the chances for survival. However, these rare events can become significant if given enough time. (As the authors note: A random mutation is like a shot in the dark; it is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance.) Teaching Tips 1. It might be interesting to discuss with students whether the Internet would have helped Mendel and Darwin. Is the Internet facilitating scientific communication? Has this technology created new problems in the process? 2. Try to find good, local examples of populations. If you live near a seashore, the many invertebrate populations (starfish, sea urchin, and kelp) would be great. Further inland we find somewhat isolated populations of fish and continuous and clumped populations of squirrels, separated by vast fields of corn, wheat, or soybeans! Bring the subject home with local examples. 3. No doubt about it, the Hardy-Weinberg equation is problematic for some students. Students should create a quick reference key to the definitions of the elements. Consider some practice problems varying the value of p and q. 4. Heterozygotes can form in two ways, the recessive from mom, the dominant from dad...or the reverse. This should serve to remind students that the 2pq portion of the equation represents the heterozygotes. 5. Another example that can be used for Hardy-Weinberg practice is cystic fibrosis. Cystic fibrosis strikes about one out of every 3300 Caucasian children. It results from the homozygous recessive condition. Thus, q2 would equal 1/3300 = and q = the square root of = The frequency of carriers = 2pq = 2 x x = = 3.42%, about one in every 29 Caucasian adults. To bring the point home to your class, divide the number of Caucasian students in your class by 29 to estimate the number of students who are carriers. (Source of information is: Fertil. Steril Jan 85(1): ) 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 Student Misconceptions and Concerns 1. Students may suggest that individuals evolve. As this chapter section clarifies, populations are the smallest units that can evolve. Individuals cannot have diversity from which to select. However, individuals can change during their lifetime in response to activities. Muscles can grow stronger because of use. However, these individual changes are not passed on to the next generation (after all, boys have been circumcised for thousands of years but are still born with a foreskin). 2. Another misperception is that evolution results from need. Challenge your students to explain how need and want have nothing to do with evolution (because neither need nor want can generate genetic variation!) 3. Students may think of mutations in a positive sense, as if they come as needed. Yet, mutations in key genes are the cause of cancer and other diseases. Only rarely does a mutation lead to a change that increases the chances for survival. However, these rare events can become significant if given enough time. (As the authors note: A random mutation is like a shot in the dark; it is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance.) Teaching Tips 1. It might be interesting to discuss with students whether the Internet would have helped Mendel and Darwin. Is the Internet facilitating scientific communication? Has this technology created new problems in the process? 2. Try to find good, local examples of populations. If you live near a seashore, the many invertebrate populations (starfish, sea urchin, and kelp) would be great. Further inland we find somewhat isolated populations of fish and continuous and clumped populations of squirrels, separated by vast fields of corn, wheat, or soybeans! Bring the subject home with local examples. 3. No doubt about it, the Hardy-Weinberg equation is problematic for some students. Students should create a quick reference key to the definitions of the elements. Consider some practice problems varying the value of p and q. 4. Heterozygotes can form in two ways, the recessive from mom, the dominant from dad...or the reverse. This should serve to remind students that the 2pq portion of the equation represents the heterozygotes. 5. Another example that can be used for Hardy-Weinberg practice is cystic fibrosis. Cystic fibrosis strikes about one out of every 3300 Caucasian children. It results from the homozygous recessive condition. Thus, q2 would equal 1/3300 = and q = the square root of = The frequency of carriers = 2pq = 2 x x = = 3.42%, about one in every 29 Caucasian adults. To bring the point home to your class, divide the number of Caucasian students in your class by 29 to estimate the number of students who are carriers. (Source of information is: Fertil. Steril Jan 85(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

(p+q)2 = p2 + 2pq + q2 = 1 (B+r)2 = B2 + 2Br + r2 = 1
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 Student Misconceptions and Concerns 1. Students may suggest that individuals evolve. As this chapter section clarifies, populations are the smallest units that can evolve. Individuals cannot have diversity from which to select. However, individuals can change during their lifetime in response to activities. Muscles can grow stronger because of use. However, these individual changes are not passed on to the next generation (after all, boys have been circumcised for thousands of years but are still born with a foreskin). 2. Another misperception is that evolution results from need. Challenge your students to explain how need and want have nothing to do with evolution (because neither need nor want can generate genetic variation!) 3. Students may think of mutations in a positive sense, as if they come as needed. Yet, mutations in key genes are the cause of cancer and other diseases. Only rarely does a mutation lead to a change that increases the chances for survival. However, these rare events can become significant if given enough time. (As the authors note: A random mutation is like a shot in the dark; it is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance.) Teaching Tips 1. It might be interesting to discuss with students whether the Internet would have helped Mendel and Darwin. Is the Internet facilitating scientific communication? Has this technology created new problems in the process? 2. Try to find good, local examples of populations. If you live near a seashore, the many invertebrate populations (starfish, sea urchin, and kelp) would be great. Further inland we find somewhat isolated populations of fish and continuous and clumped populations of squirrels, separated by vast fields of corn, wheat, or soybeans! Bring the subject home with local examples. 3. No doubt about it, the Hardy-Weinberg equation is problematic for some students. Students should create a quick reference key to the definitions of the elements. Consider some practice problems varying the value of p and q. 4. Heterozygotes can form in two ways, the recessive from mom, the dominant from dad...or the reverse. This should serve to remind students that the 2pq portion of the equation represents the heterozygotes. 5. Another example that can be used for Hardy-Weinberg practice is cystic fibrosis. Cystic fibrosis strikes about one out of every 3300 Caucasian children. It results from the homozygous recessive condition. Thus, q2 would equal 1/3300 = and q = the square root of = The frequency of carriers = 2pq = 2 x x = = 3.42%, about one in every 29 Caucasian adults. To bring the point home to your class, divide the number of Caucasian students in your class by 29 to estimate the number of students who are carriers. (Source of information is: Fertil. Steril Jan 85(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. Student Misconceptions and Concerns 1. Students may suggest that individuals evolve. As this chapter section clarifies, populations are the smallest units that can evolve. Individuals cannot have diversity from which to select. However, individuals can change during their lifetime in response to activities. Muscles can grow stronger because of use. However, these individual changes are not passed on to the next generation (after all, boys have been circumcised for thousands of years but are still born with a foreskin). 2. Another misperception is that evolution results from need. Challenge your students to explain how need and want have nothing to do with evolution (because neither need nor want can generate genetic variation!) 3. Students may think of mutations in a positive sense, as if they come as needed. Yet, mutations in key genes are the cause of cancer and other diseases. Only rarely does a mutation lead to a change that increases the chances for survival. However, these rare events can become significant if given enough time. (As the authors note: A random mutation is like a shot in the dark; it is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance.) Teaching Tips 1. It might be interesting to discuss with students whether the Internet would have helped Mendel and Darwin. Is the Internet facilitating scientific communication? Has this technology created new problems in the process? 2. Try to find good, local examples of populations. If you live near a seashore, the many invertebrate populations (starfish, sea urchin, and kelp) would be great. Further inland we find somewhat isolated populations of fish and continuous and clumped populations of squirrels, separated by vast fields of corn, wheat, or soybeans! Bring the subject home with local examples. 3. No doubt about it, the Hardy-Weinberg equation is problematic for some students. Students should create a quick reference key to the definitions of the elements. Consider some practice problems varying the value of p and q. 4. Heterozygotes can form in two ways, the recessive from mom, the dominant from dad...or the reverse. This should serve to remind students that the 2pq portion of the equation represents the heterozygotes. 5. Another example that can be used for Hardy-Weinberg practice is cystic fibrosis. Cystic fibrosis strikes about one out of every 3300 Caucasian children. It results from the homozygous recessive condition. Thus, q2 would equal 1/3300 = and q = the square root of = The frequency of carriers = 2pq = 2 x x = = 3.42%, about one in every 29 Caucasian adults. To bring the point home to your class, divide the number of Caucasian students in your class by 29 to estimate the number of students who are carriers. (Source of information is: Fertil. Steril Jan 85(1): )

Examples of Evolution by Natural Selection

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