MACROEVOLUTION Student Packet SUMMARY EVOLUTION IS A CHANGE IN THE GENETIC MAKEUP OF A POPULATION OVER TIME Macroevolution refers to large-scale

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1 MACROEVOLUTION Student Packet SUMMARY EVOLUTION IS A CHANGE IN THE GENETIC MAKEUP OF A POPULATION OVER TIME Macroevolution refers to large-scale evolutionary changes such as speciation events, origin of key adaptations, and impacts of mass extinctions on the diversity of life. The five basic evolutionary mechanisms natural selection, gene flow, mutations, non-random mating, and genetic drift can produce major evolutionary change if given enough time. EVOLUTION IS SUPPORTED BY EVIDENCE FROM MANY DISCIPLINES, INCLUDING MATHEMATICS Sources of evidence include: 1. Direct observation of evolutionary change, e.g., observations and measurements of development of antibiotic and pesticide resistance. 2. Fossil record shows that past organisms differ from present day organisms. Fossils can be dated by a variety of methods that provide evidence for evolution. These include the age of the rocks where a fossil is found, the rate of decay of isotopes including carbon-14, the relationships within phylogenetic trees and geographical data. 3. Homologous structures show common ancestry. Vestigial structures are homologous structures that lost their original function, such as the femur in whales. Vestigial structures can be compared to fossils and provide evidence for evolution. 4. Embryonic development also shows common ancestry. 5. Molecular biology shows that closely related organisms have similar DNA sequences and similar amino acid sequences. ORGANISMS ARE LINKED BY LINES OF DESCENT FROM COMMON ANCESTRY Organisms share many conserved core processes and features that evolved and are widely distributed among organisms today. For example: DNA and RNA are carriers of genetic information through transcription and translation in all organisms. Molecular building blocks are common in all life forms. Major features of the genetic code are shared by all modern living systems. Metabolic pathways are conserved across all currently recognized domains. Homeostatic control systems in microbes, plants and animals support common ancestry. Continuity of homeostatic mechanisms reflects common ancestry, while changes may occur in response to different environmental conditions. SPECIATION AND EXTINCTION HAVE OCCURRED THROUGHOUT THE EARTH S HISTORY AND CONTINUE TO OCCUR Speciation is the process by which one species splits into two or more daughter species, which thereafter evolve as distinct lineages. The biological species concept distinguishes species on the basis of reproductive isolation while the morphological species concept distinguishes species on the basis of physical similarities. In order for speciation to take place, reproductive isolation must occur. Reproductive isolation increases with increasing genetic divergence between populations. Two common types of speciation are allopatric and sympatric speciation. Allopatric speciation results when populations are separated by a physical barrier. This type of speciation may follow founder events, in which some members of a population cross a barrier and start a new isolated population. In sympatric speciation, a new species originates while remaining in the same geographic area as the parent species. Many plant species have evolved sympatrically through polyploidy by an increase in the number of 1

2 chromosome sets due to nondisjunction in meiosis. Sympatric speciation can also result from habitat shifts and sexual selection. Reproductive isolation is reinforced by prezygotic or postzygotic barriers. Prezygotic isolating mechanisms prevent formation of a zygote (hybridization). Prezygotic mechanisms include habitat, temporal, behavior, mechanical and gametic isolation. Postzygotic isolating mechanisms, such as reduced hybrid viability, reduced hybrid fertility or hybrid breakdown, reduce the fitness of hybrids. Speciation rates can vary from a few thousand years to tens of millions of years. Gradualism proposes that species descended from a common ancestor and gradually diverge more and more in morphology as they acquire unique adaptations. Punctuated equilibrium is used to describe periods of apparent stasis interrupted by sudden change observed in the fossil record. Adaptive radiation is the process in which organisms diversify rapidly into a multitude of new forms. Starting with a recent single ancestor, this process results in the speciation and phenotypic adaptation of an array of species exhibiting different morphological and physiological traits with which they can exploit a range of divergent environments. Adaptive radiations may follow mass extinctions. They have also occurred in groups of organisms that possessed major evolutionary innovations or that colonized new regions in which there was little competition. Species extinction rates are high at time of ecological stress. Evolutionary history has been punctuated by five mass extinctions that radically altered the history of life. Some of these extinctions may have been caused by changes in continent positions, volcanic activity or impacts from meteorites or comets. EVIDENCE SUPPORTS SEVERAL HYPOTHESES ABOUT ORIGIN OF LIFE ON EARTH Geological evidence provides support that the Earth formed about 4.6 bya and the earliest fossil evidence for origin of life dates to 3.5 bya. Primitive Earth provided inorganic precursors from which simple organic molecules could have been synthesized due to the presence of available free energy and the absence of oxygen. The joining of monomers produced polymers with the ability to replicate, store and transfer information. These complex reaction sets could have occurred in solution (organic soup model) or as reactions on solid reactive surfaces. The RNA World hypothesis proposes that RNA could have been the earliest genetic material. LIFE CONSISTS OF THREE DOMAINS THAT SHARE A COMMON ANCESTOR Molecular and genetic evidence indicate that all organisms on Earth share a common ancestral origin of life. Two of life s three domains, Bacteria and Archaea, are prokaryotic. They are distinguished from Eukarya by lack of a nucleus and lack of membrane-bound organelles. Eukaryotes are related to both Archaea and Bacteria and are thought to have formed through endosymbiosis. The endosymbiotic theory proposes that mitochondria and chloroplasts were formerly small prokaryotes that began living within a larger cell. 2

3 MULTIPLE CHOICE QUESTIONS 1. Asteroids contain an element normally not found on Earth called iridium. The asteroid that hit the Earth 65 million years ago contained iridium and a layer of iridium is found around the impact zone. This zone of rock is called the K-T (Cretaceous-Tertiary) boundary and it is hypothesized that the consequences of the impact have caused the extinction of dinosaurs. Which of the following would be the most reasonable plan for a student to follow in order to search for fossils from the Mesozoic era of dinosaurs? a. Collecting fossils from rock layers located above the rocks with the highest amount of iridium. b. Searching any horizontal rock layer and trying to find those that contain the largest number of fossils. c. Looking in sedimentary rock layers deposited prior to the formation of K-T boundary. d. Searching in rock layers deposited after the formation of the K-T boundary. 2. In 1953, Stanley Miller and Harold Urey performed experiments to model early Earth s atmosphere. They discharged electric sparks into a chamber containing water vapor, methane, hydrogen gas and ammonia. The experiments yielded a variety of amino acids found in organisms today. These results best support which of the following hypothesis? a. Oxygen was a necessary element for formation of organic molecules on Earth. b. Conditions on the young Earth were sufficient for the formation of organic molecules. c. The molecules necessary for life did not exist at the time when Earth was formed. d. Organic molecules that make up living organisms were brought to Earth by a comet. 3. Today, all known prokaryotic and eukaryotic organisms contain DNA as genetic material. However, it is hypothesized that the first genetic material was most likely RNA, not DNA. What is the most plausible reason for the switch from RNA containing protocells to DNA based genetic systems during the evolution of life on Earth? a. RNA is involved with transcription and translation in protein synthesis and cannot provide multiple functions. b. DNA forms the rod-shaped chromosomes necessary for cell division. c. RNA performs many enzyme-like catalytic functions and replicates too fast to support life. d. DNA is chemically more stable and replicates with fewer errors than RNA. 4. Many scientific disciplines provide evidence for the modern concept of evolution. Which of the following sequences is arranged appropriately from the earliest to the most recent event as supported by evidence? a. Origin of Earth, beginning of the accumulation of atmospheric oxygen, origin of prokaryotes, oldest eukaryotic cell fossils, origin of multicellular eukaryotes, colonization of land by plants and fungi, first land animals evolve. b. Origin of Earth, origin of prokaryotes, beginning of the accumulation of atmospheric oxygen, oldest eukaryotic cell fossils, origin of multicellular eukaryotes, colonization of land by plants and fungi, first land animals evolve. c. Origin of Earth, origin of prokaryotes, oldest eukaryotic cell fossils, beginning of the accumulation of atmospheric oxygen, origin of multicellular eukaryotes, colonization of land by plants and fungi, first land animals evolve. d. Origin of Earth, origin of prokaryotes, oldest eukaryotic cell fossils, origin of multicellular organisms, colonization of land by plants and fungi, beginning of the accumulation of atmospheric oxygen, first land animals evolve. 3

4 5. Punctuated equilibrium was first proposed by the Harvard biology professor Steven Jay Gould in order to explain how some species appear in the geologic time scale. According to this model, a. given enough time, most existing species will gradually branch into new species. b. most evolution occurs through sympatric speciation. c. most new species accumulate their unique features relatively rapidly as they come into existence, then change little for the rest of their duration as a species. d. history of life on Earth has been punctuated by five major extinctions. 6. The diagram on the right shows an example of gene duplication. Which of the following is an incorrect statement about this type of mutation? a. Gene duplication is a major mechanism through which new genetic material is generated during evolution. b. Gene duplication is a type of point mutation. c. In gene duplication, a long stretch of DNA is copied, followed by point mutations that change one or both of the copies of the gene. d. Gene duplication creates a situation in which one copy of the gene maintains its original function, while the duplicate may evolve a new function. 7. The volcanic Hawaiian Islands, in the middle of the Pacific Ocean, are in many ways very similar, in terms of evolution, to the volcanic Galapagos Islands, also located in the Pacific Ocean. While each has differing species, the underlying evolutionary processes affecting them are similar. These islands are a great showcase of evolution because of intense a. adaptive radiation and allopatric speciation. b. reproductive isolation and sympatric speciation. c. polyploidy and sympatric speciation. d. hybrid vigor and allopatric speciation. 4

5 MATH GRID IN 1. Scientists use various methods to establish the age of fossils. One such method, for fossils less than 75,000 years old, is to compare the amount of radioactive carbon-14 to normal carbon-12. Both forms of carbon are assimilated in to the organism as it feeds over time. When the organism dies, it quits accumulating carbon in its body. Over time, carbon-14 is converted to nitrogen-14. If the half-life of carbon-14 is 5,730 years, then a fossil that has one-eighth the normal proportion of carbon-14 to carbon-12 is probably how many years old? Give your answer to the nearest whole number. 2. Allopolyploid is a fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes. Plant species A has a diploid number of 12 and plant species B has a diploid number of 16. A new species, C, arises as an allopolyploid from A and B. Determine the haploid number for species C. Give your answer to the nearest whole number. 5

6 SHORT FREE RESPONSE QUESTIONS 1. Populations of a plant species have been found growing in the mountains at altitudes above 2,500 meters. Populations of a plant that appears similar, with slight differences, have been found in the same mountains at altitudes below 2,300 meters. a. Describe TWO kids of data that could be collected to provide a direct answer to the question, do the populations growing above 2,500 meters and the populations growing below 2,300 meters represent a single species? b. Explain how the data you suggested in part a. would provide a direct answer to the question. 2. Discuss TWO mechanisms of speciation that lead to the development of separate species from a common ancestor. 6

7 LONG FREE RESPONSE QUESTION Biologists are interested in preserving the diversity of living organisms on the planet. a. Explain THREE of the following processes or phenomena, using an appropriate example for each. Mutation Adaptive radiation Polyploidy Population bottlenecks Growth of the human population b. For each process or phenomenon you selected in part a., discuss its impact on the diversity of life on Earth. 7

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