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Transcript
Unit 5 Study Guide Chapters 22-25 Evolution All questions within each section of the Unit Study Guide will be due on the day of the unit exam. Each section should be clearly labeled by section number and number of question for complete points. 5–1: Read 438—446 Natural Selection Pages 438 – 442 put Darwin’s ideas into historical context, no need to spend too much time on this except: be able to state Lamarck’s idea of evolution. Taxonomy is the branch of biology dedicated to the naming and classification of all forms of life. Carolus Linnaeus developed binomial nomenclature, a two-part naming system that includes the organism’s genus and species. Jean-Baptiste de Lamarck developed an earl theory of evolution, which in part stated that characteristics acquired during an organism’s lifetime could be passed on to the next generation. Our modern understanding of genetics provides no evidence that this is possible. Darwin’s idea about how organisms evolve, natural selection, is highlighted in the yellow box on page 444 and summarized later in the text. You must know this well! Darwin’s view of life as expressed in The Origin of Species (1859) contrasted sharply with traditional beliefs of an Earth only a few thousand years old, populated by forms of life that has been created at the beginning and remained unchanged ever since. The concept of natural selection states that a population can change over generation if individuals with certain heritable traits produce more viable offspring than other individuals. The result of natural selection is evolutionary adaptation, which is an accumulation of inherited characteristics that enhance organisms’ ability to survive and reproduce in in specific environments. Natural Selection can work only on heritable traits, traits that are passed from organisms to their offspring. Questions: 1. Describe Lamarck’s view of evolution. How would you argue against it with your present knowledge of genetics and molecular biology? 2. The word evolution was not used in Darwin’s publication; instead, he used “decent with modification.” Explain what Darwin meant by this term. 3. Describe three inferences Darwin made from his observations that lead him to propose natural selection as a mechanism for evolutionary change. 4. Thoroughly explain the concept of natural selection. Summarize with one sentence stressing the most important idea in the theory of natural selection. 5. Explain why an individual organism cannot evolve. 1 5–2: Read 446—451 The Evidence As you read examples of natural selection, remember that it operates on chemical traits as well as those more obviously visible. The section beginning with Homology. . . on page 448 describes what is sometimes referred to as “the evidence for evolution by natural selection.” What is referred to as “molecular homology” is often listed separately from the physical homology described in Fig 11.15. You should be able to define these four categories of evidence, offer examples of each and state how it supports evolutionary theory: Homologous structures, Vestigial organs, Molecular homology, Biogeography. - Note: The fossil record is also considered to be evidence for evolution, as well, but in this text it is mentioned separate and earlier in section 22.1. Darwin’s theory of evolution through natural selection explains the succession of forms in the fossil record. Transitional fossils have been found that link ancient organisms to modern species, just as Darwin’s theory predicts. Questions: 1. Describe examples of natural selection. 2. List the four categories of, and explain, the evidence for evolution. 3. Do whales really need all those bones in their flippers? Explain. 4. In Fig 22.16, what conclusion can be reached about the relationship of humans to mice as compared to that between humans and frogs? 5. How does a scientific theory differ from the general use of the term theory? 5–3 Read 454—458 Hardy-Weinberg Equilibrium Be sure you understand the terms population, gene pool and, especially, allele frequency. Frequency is usually expressed as a decimal quantity showing “parts out of one” (the total) but can also be expressed as a percent (parts out of one hundred). Note that, in addition to allele frequencies, the concept of frequency can also be applied to phenotypes and genotypes. You must know the Hardy-Weinberg theorem, the two equations describing it and how to do problems involving allele frequencies. The Hardy-Weinberg theorem is used to describe a population that is NOT evolving. It states that the frequencies of alleles and genes in a population’s gene pool will remain constant over the course of generations unless they are acted upon by forces other than Mendelian segregation and the recombination of alleles. Fig 23.5 is an example of how to apply the mathematics of Hardy-Weinberg. Notice that even though the diagram looks like a Punnett square, it is referring to possible outcomes in an entire population instead of possible offspring from a single pair of parents. The diagram should help you see how the H-W math is used to calculate different frequencies. (At the top, we see the allele frequencies. At the bottom, we see the frequency of the different genotypes. The yellow box, page 458, states the conditions for H-W equilibrium. Pedit states (old AP Bio teacher), “Every good biology student knows these [H-W conditions] or dies slowly on tests, flounders in misunderstanding and gives birth to half-baked children whose only dream is to join the circus.” (hahaha, I saw this on one of Mr. Pedit’s old worksheets and thought it was hilarious!) HARDY-WEINBERGY WILL BE ON YOUR AP EXAM!!! KNOW THE MECHANISMS AND MATHEMATICAL APPLICATIONS!!!!!!! 2 Questions 5-3: 1. Describe the Hardy–Weinberg equilibrium in words and with mathematics. 2. State the conditions are necessary for the Hardy–Weinberg equilibrium to hold true. 3. Use the H-W equation to calculate allele frequencies when the frequency of homozygous recessive individuals in a population is 25% 4. Explain why meiosis and random fertilization alone will not alter the frequency of alleles or genotypes in a population. 5–4: Read 459—470 Microevolution Today we define evolutionary change on it smallest scale as microevolution. Microevolution is change in the genetic makeup of a population from generation to generation. It refers to adaptations that are confined to a single gene pool. New genes and new alleles originate only by mutations, which are changes in the nucleotide sequence of DNA. Because mutations in somatic cells disappear when the individual dies, only mutations in somatic cells disappear when the individual dies, only mutations in cell lines that produce gametes can be passed to offspring. Mutation has two roles. It is a H-W factor and can contribute to changes in gene frequencies. But it also has the all-important role of adding new alleles and genes to populations. Recombination is also important in bringing new combinations of existing alleles together for yet more variation for natural selection to act upon. Natural selection is, by far, the most important H-W factor. Why? Genetic drift is also quite important, especially when considering how a new population might get established. Genetic drift is the unpredictable fluctuation in allelic frequencies from one generation to the next. The smaller the population, the greater the chance is for genetic drift. Examples of genetic drift: - Bottleneck effect = sudden change in environment (ex. earthquake, flood, fire) drastically reduces the size of a population. The few survivors that pass through the restrictive bottleneck may have a gene pool that no longer reflects the original population’s gene pool. - Founder effect = occurs when a few individuals become isolated from a larger population and establish a new population whose gene pool is not reflective of the source population. Section 23.4 makes an important point but is a bit long winded. Read lightly to get the idea; focus on: - Figures 23.11 and 23.12 - “Heterozygous Advantage”, page 466 - Page 469, “Why Natural Selection. . .”. Notice the role of genetic drift. Questions: 1. List and explain the five factors that can shift the Hardy–Weinberg equilibrium (= causes of microevolution). 2. Which factor do you think is most important? Why? 3. Genetic variation: what is it, what are the sources, how is it maintained? 4. Explain how, and upon what, natural selection acts and with what results. 5. Explain how diploidy can protect a rare recessive allele from elimination by natural selection. 6. Explain what is meant by heterozygote advantage and give an example. How does this affect allele frequencies? 7. Is all selection done by environmental factors? Explain. 8. Explain how female preferences for showy male traits may benefit the female. 9. Explain how the genetic variation promoted by sex may be advantageous to individual on a generational time scale. 3 5–5: Read 472—480 [up to “Adaptive Radiation”] Speciation Speciation is the process by which new species arise. Fig 24.2: don’t sweat the terms. The difference is the left side shows the formation of a new species over time. The right show how one species can eventually produce two separate species. This chapter is about how enough changes (or even the right single change) can result in speciation. To understand this, you need to know what is meant by species. Since species are different due to different alleles (and entire genes if more distantly related), then something has to prevent the alleles from mixing (“gene flow”) if two species are to develop from one. The populations, or sub=populations, that are to go on to become different species must be reproductively isolated. This is the key. Different types of reproductive barriers are shown in Fig. 24.4: Focus on the “prezygotic barriers”, have a passing knowledge of the postzygotic barriers. Skim the sections on Polyploidy and Habitat Differentiation. But, do be able to distinguish between, and give examples of, allopatric and sympatric speciation. Questions: 1. Define species in the biological sense. What problems exist with this definition? 2. List and explain five mechanisms that can isolate populations. (You can consider the postzygotic barriers together.) 3. Describe the process through which allopatric speciation and sympatric speciation may occur. 4. Give an overview as to the necessary conditions for speciation to occur. 5–6: Read 480—488 Macroevolution Adaptive radiation is what started it all (i.e., Darwin’s finches). Adaptive radiation occurs when many new species arise from a single common ancestor. It typically occurs when a few organisms make their way to new, distant areas or when environmental changes cause numerous extinctions, opening up ecological niches for the survivors. Section 24.3 adds nothing new as far as basic concepts. Macroevolution simply refers to the same evolutionary principles acting over very long periods of time to produce large changes. The main addition might be this: although recombination might be enough to produce speciation, the great diversity of life seen today also requires mutations and chromosomal rearrangements. Early arguments against evolutionary theory centered around: How could something as complicated as the eye, obviously requiring many genes, “evolve” when many different evolutionary events are required and unlikely to have all occurred together. Fig 24.14 shows that it doesn’t take a complete modern eye to offer some adaptive function. Can you think of how just the “patch of pigmented cells” shown in (a) might be advantageous? Pay special attention to Evolution is Not Goal Oriented (using Fig 24.20 as an example). How does this apply to the eye in Fig 24.14? Punctuated equilibrium is a term used to describe periods of apparent stasis punctuated by sudden change observed in the fossil record. Homeotic genes determine the location of and organization of body parts. Hox genes are one class of homeotic genes. Changes in Hox genes and in the genes that regulate them can have a profound effect on morphology, thus contributing to the potential for evolutionary change. Questions: 1. What is meant by punctuated equilibrium? What might this have to do with so called “gaps” in the fossil record? 2. Describe how each step in the evolution of the complex eye might bestow an evolutionary advantage to its owner. 3. How do the roles of natural selection and genetic drift figure into the discussion of evolution not being goal oriented? 4 5–7: Read 491—508 Classification and Phylogeny Fig 25.2: whoa! By now you should be able to read the thick green lines as saying: humans share a more recent common ancestor with fungi than they do with plants. Must be due to something more fundamental that outward appearance. You should be able to distinguish analogous structures from homologous structures and offer examples of each. Understand why each arises. Convergent evolution has taken place when two organisms developed similarities as they adapted to similar environmental challenges – not because they evolved from a common ancestor. The likenesses that result from convergent evolution are considered analogous rather than homologous. For example, the four-chambered heart of birds and mammals is analogous. The most recent common ancestor of birds and mammals had a three-chambered heart. The comparison of different genes and proteins (molecular systematics) of organisms allows us to determine evolutionary relationships on a molecular level. The more alike the DNA sequences of two organisms are, the more closely related they are evolutionarily. Fig 25.8 outlines the system of classifying organisms into broader, more inclusive groups (going down the chart). But Fig 25.9 puts some meaning on the usefulness of classifying in this way. Be sure you understand this and the two related diagrams in the text. The hierarchical classification of organisms consists of the following levels (in order of decreasing broadness): domain, kingdom, phylum, class, order, family, genus, species Focus on the section on Cladistics including Fig’s 25.10 and 25.11(b). Skim 499 – 507 [The Universal. . .] except for these points: - In fig 25.13, note how times since the common ancestor can be found from the fossil record and using “molecular clocks” - Fig 25.17 serves as a reminder of how new genes can develop fueling evolution. - Briefly know what a molecular clock is. Fig 25.18 is even more shocking than Fig 25.2. Read this sub-section in detail Molecular clocks are methods used to measure the absolute time of evolutionary change based on the observation that some genes and other regions of the genome appear to evolve at constant rates. Questions: 1. List the levels of classification. Which are used to name organisms? 2. Compare and contrast homology and analogy. Explain why it is crucial to distinguish between homology and analogy before selecting characters to use in the reconstruction of phylogeny. 3. How can proteins and DNA be used to compare species? 4. Does the apparent discontinuity of the fossil record (e.g.: horses) bother biologists? Explain. 5. What is the defining characteristic of a cladogram? What advantage does cladistics offer over earlier methods of classifying critters? 6. Describe the evidence that suggests there is a universal tree of life. 7. Explain how molecular clocks are used to determine the approximate time of key evolutionary events. Explain how molecular clocks are calibrated in actual time. 8. Describe some limitations of molecular clocks. 5