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Transcript
Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory Discuss the validity of the following statement: When scientists speak of evolutionary theory, the word “theory” has the same meaning as it does in everyday language, referring to the fact that evolutionary theory is just an idea that is not proven and backed by scientific evidence. Concept 15.1 Evolution Is Both Factual and the Basis of Broader Theory Consider the validity of the following statement and then select a correct answer from the options given: When scientists speak of evolutionary theory, the word “theory” has the same meaning as it does in everyday language, referring to the fact that evolutionary theory is just an idea that is not proven and backed by scientific evidence. a. True b. False c. I don’t understand the question. Concept 15.2 Mutation, Selection, Gene Flow, Genetic Drift, and Random Mating Result in Evolution Discuss the following scenarios with reference to whether or not they correctly describe examples of the process we attribute to having been first described by Charles Darwin - evolution by “natural selection”: • The development of a curved back over the period of your lifetime • Giraffes’ necks lengthening during their lifetime as they reach up to high branches to eat the leaves of trees • A drought affects an island where a population of a particular finch species lives. The species naturally has a small amount of variability in bill (beak) size. The drought results in finches with larger bills surviving at a greater rate than those with smaller bills, since the larger billed birds can crack open and eat very tough seeds that the small billed individuals cannot. • A mutation in an insect results in increased digestive efficiency that allows females to obtain more energy from their food, and convert that energy into larger eggs that are more likely to survive, resulting in these females producing more surviving offspring Concept 15.2 Mutation, Selection, Gene Flow, Genetic Drift, and Random Mating Result in Evolution Which of the following scenarios correctly describe examples of the process we attribute to having been first described by Charles Darwin - evolution by “natural selection”: a. The development of a curved back over the period of your lifetime b. Giraffes’ necks lengthening during their lifetime as they reach up to high branches to eat the leaves of trees c. A drought affects an island where a population of a particular finch species lives. The species naturally has a small amount of variability in bill (beak) size. The drought results in finches with larger bills surviving at a greater rate than those with smaller bills, since the larger billed birds can crack open and eat very tough seeds that the small billed individuals cannot. d. A mutation in an insect results in increased digestive efficiency that allows females to obtain more energy from their food, and convert that energy into larger eggs that are more likely to survive, resulting in these females producing more surviving offspring e. Both c and d Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies Consider and discuss the following scenarios in relation to Hardy–Weinberg equilibrium, and determine whether or not allele frequencies are likely to change, leading to evolution: • An isolated and highly endangered population of 50 woodland caribou • A large population of lizards whose males have red, blue, or green tails; females preferentially mate with red-tailed males • A large population of fish in an isolated lake; every 5 years a flood results in some fish from a population in an adjacent lake mixing with this population Concept 15.3 Evolution Can Be Measured by Changes in Allele Frequencies In which of the following scenarios are allele frequencies are likely to change, leading to evolution, according to Hardy–Weinberg assumptions: a. An isolated and highly endangered population of 50 woodland caribou b. A large population of lizards whose males have red, blue, or green tails; females preferentially mate with red-tailed males c. A large population of fish in an isolated lake; every 5 years a flood results in some fish from a population in an adjacent lake mixing with this population d. All of the above e. None of the above Concept 15.4 Selection Can Be Stabilizing, Directional, or Disruptive A flock of 150 tiny orange and brown sparrows is blown off course and ends up on a huge island where there is a lot of open shrubby land adjacent to low hills with trees. There are mammals, many plants, some insects, lizards, and a few hawks, but there are no other small birds. There are two types of plants with seeds edible for the sparrows: a small-seeded tree and a large-seeded bush. Discuss what you think might happen to this population of birds over many generations with respect to the three different types of selection discussed in the text: • Stabilizing • Directional • Disruptive Concept 15.4 Selection Can Be Stabilizing, Directional, or Disruptive What you think might happen to this population of birds over many generations (refer to graphs below)? a. Stabilizing selection will operate on population beak size. b. Directional selection will operate on population beak size. c. Disruptive selection will operate on population beak size. d. Population beak size will not change; the birds will maintain their original genetic diversity. A B C Concept 15.5 Genomes Reveal Both Neutral and Selective Processes of Evolution In a population of size N of a diploid organism, the rate of fixation of neutral mutations () in this population is given by the equation: From this equation, discuss what can we deduce about the influence of population size (N) on the rate of fixation of neutral mutations in a population. Concept 15.5 Genomes Reveal Both Neutral and Selective Processes of Evolution In a population of size N of a diploid organism, the rate of fixation of neutral mutations () in this population is given by the equation: From this equation, we can deduce that population size (N) has _______ on the rate of fixation of neutral mutations? a. an important effect b. no effect c. I don’t understand the question. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features Why sex is good Scientists have long puzzled over why sex has evolved, given the disadvantages of sex: 1. Gene mixing tends to break up favorable combinations, and why break up a good thing? 2. Asexual reproduction is twice as efficient as sexual reproduction at passing on genes to the next generation. Every time a sexual mother produces a child, only one-half of the child’s genes come from the mother; the other half are from the father. Reproducing parthenogenetically, an asexual mother passes on to her child a complete copy of her genes. It stands to reason that such populations should rapidly out-reproduce a sexual population, since every individual is a female that can reproduce offspring. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features Why sex is good (continued) For these two reasons, it seems clearly disadvantageous for individuals to reproduce sexually! Yet sex has evolved and some kind of genetic recombination (sex) occurs and retained in most organisms. German biologist August Weismann proposed one possible explanation for this conundrum, suggesting that sex increases advantageous genetic variation. When two different individuals mate by joining their gametes together, they produce a brand new genetic mixture and this promotes evolutionary adaptation. In other words, sex is good because it allows you to evolve more quickly when conditions change. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features Why sex is good (continued) A team of scientists at the Imperial College London investigated the hypothesis that the genetic recombination that results from sexual reproduction is advantageous. They published their results in Nature magazine in March 2005. They performed an experiment on yeasts, which are single-celled fungi. Yeasts can reproduce both sexually and asexually, are easy to keep in the lab, and reproduce rapidly. Yeasts normally reproduce asexually, but will reproduce sexually when they are stressed (starved, high temperatures, etc.). The team of scientists did not want this sexual/asexual switching to occur so they genetically manipulated one asexual strain. They deleted the two genes required for normal meiosis, so that sexual reproduction was impossible. Now they had two pure strains of yeast—an asexual strain and a sexual strain. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features Why sex is good (continued) The team compared the reproductive rate of the asexual vs. the sexual yeasts in two different environments: one benign and one harsh. • The benign environment had plenty of nutrients although glucose was limited so that growth was not uncontrolled. • The harsh environment had the same glucose concentration but was at a higher temperature and had more demanding osmotic conditions (e.g., the water was more salty). Evolutionary “fitness” was measured by comparing the growth rate of the asexual and sexual strains of yeast. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features On the graph below, plot the results you would expect if Weismann’s hypothesis were correct. Plot the changes in fitness values over time in the populations of sexual yeasts in benign conditions, asexual yeasts in benign conditions, asexual yeasts in harsh conditions, and sexual yeasts in harsh conditions. Concept 15.6 Recombination, Lateral Gene Transfer, and Gene Duplication Can Result in New Features From this graph showing the experimental results of growing genetically manipulated sexual and asexual yeast strains in harsh versus benign conditions, we can interpret that: a. Sexual reproduction is advantageous in harsh environments. b. Asexual reproduction is always equally advantageous to sexual reproduction. c. Asexual reproduction is always advantageous to sexual reproduction. d. There is no difference in fitness between sexual and asexually reproducing yeasts. e. Sexual reproduction is always advantageous to asexual reproduction. Concept 15.7 Evolutionary Theory Has Practical Applications Discuss the validity of following statements given what you have learned about evolution: • Pesticide resistance exhibited by insects in agricultural settings provides direct evidence that evolution is occurring. • Antibiotic resistance is an example of evolution that helps to keep pharmaceutical companies in business. • In vitro evolution at the molecular level, as described in Figure 15.23 of the textbook, is analogous to the artificial selection of pigeons and dogs that Darwin was interested in more than two centuries ago. Concept 15.7 Evolutionary Theory Has Practical Applications Given what you have learned about evolution, which of the following statements is true? a. Pesticide resistance exhibited by insects in agricultural settings provides direct evidence that evolution is occurring. b. Antibiotic resistance is an example of evolution that helps to keep pharmaceutical companies in business. c. In vitro evolution at the molecular level, as described in Figure 15.23 of the textbook, is analogous to the artificial selection of pigeons and dogs that Darwin was interested in more than two centuries ago. d. All of the above e. None of the above