BSC2011 Summer 2013 Exam #3 Study Guide !1 Unit III: Evolution & Population Genetics 1. What is the biological meaning of the term “evolution”? Contrast microevolution with macroevolution. Evolution • Species change over time • New species arise by the modification of earlier species o “Descent with modification” • Evolution = changes in the frequencies of alleles in a population • Not goal-oriented Microevolution Macroevolution - the gradual evolution of traits within a population of a species over time - not disputed (can be observed today) - the evolution of an entirely new species - disputed (has not occurred recently) 2. Describe/explain how each of the following serves as evidence that evolution could be a means by which life’s diversity arose: artificial selection, comparative anatomy, paleontology, and comparative embryology. Artificial Selection • New species are created from a common ancestor via selective breeding by humans Comparative Anatomy • The anatomy of different organisms could be similar because they descended from a common ancestor • Ex) Mammals have the same bones in the same relative positions in their forelimbs, which suggests that mammals evolved from a common ancestor who had this basic forelimb groundplan o Forelimbs later evolved different functions in different groups of mammalsBSC2011 Summer 2013 Exam #3 Study Guide !2 Paleontology • Paleontology: The study of fossils • The pattern of fossils in rock strata (layers) suggests that organisms have changed (evolved) over time • Fossil organisms in close (more recent) layers are similar, but still different • Fossil organisms in farther apart layers are less similar • New species appear in upper layers that didn't exist in lower layers • Many species in older (lower) layers don’t exist today (extinct) Comparative Embryology • Early embryos of different vertebrates share many general features • von Baer’s Law: As development proceeds, similarity persists only among more closely related vertebrates • Ex) Reptile & human early embryos are similar, but pig and human later embryos still look similar (whereas those of reptiles do not) lizard turtle pig humanBSC2011 Summer 2013 Exam #3 Study Guide !3 3. How can molecular biology provide evidence for evolution? Provide two examples. • Protein & DNA sequence comparisons o The more recently two species shared a common ancestor, the more similar their proteins & DNA o Ex) Humans and monkeys share ~95% of their genetic content, and shared a common ancestor more recently than humans & mice (87%) 4. Distinguish between homologous, analogous, and vestigial structures, providing at least one example of each. • Homologous Structures: Structures that share similarities because of common ancestry o Look similar, but many have evolved for different functions • Analogous Structures: Structures that have a similar function, but not because of common ancestryBSC2011 Summer 2013 Exam #3 Study Guide !4 o Ex) Wings of birds and wings of insects • Vestigial Structures: “Remnants” of once functional ancestral structures o Ex) Hindlimbs of whales & snakes o Ex) Human appendix, tail bone, goose bumpsBSC2011 Summer 2013 Exam #3 Study Guide !5 5. What did Darwin find intriguing about the finches on the Galapagos Islands? Explain why/how the Galapagos finches might have helped Darwin formulate his hypothesis of evolution by natural selection? • Darwin noticed that the species of finch that lived close together appeared similar, and species living in the same kind of habitat but in different locations did not o The most notable difference was the size & shape of their beaks • He concluded that, while they had descended from a common ancestor (on the mainland), new species of finch had arisen through adaptive radiation • Adaptive Radiation: When members of an ancestral species “radiate” (move into) new environments and eventually become several new species, each adapted to a particular lifestyle • Genetic variability within species made finches with certain beaks more suited to their environment and the type of food available o Ex) Thin, sharp beaks were ideal for consuming insects o Ex) Short, powerful beaks were ideal for crushing seeds • The offspring of finches whose beaks were more adapted to facilitating the consumption of the food available were more “fit,” and survived and produced more offspring than those whose beaks had not adapted, passing on the genes for the modified beaks o This is an example of natural selection, because in the competition for resources, those who were better equipped to feed “won” • The finches who lived on different islands could not interbreed, so they eventually became distinct speciesBSC2011 Summer 2013 Exam #3 Study Guide !6 6. Describe the process by which populations evolve via natural selection. Why is it said that genetic variation is a prerequisite (is required) for evolution by natural selection? Darwin’s Model of Natural Selection • Within a population, more offspring are produced than can survive to reproduce o This leads to competition for resources and a struggle for existence • Variation exists in all organisms, and much of this variation is heritable (genetic) • Some of this variation affects an individual’s ability to survive and reproduce o Who survives to reproduce is not random • The “fittest” individuals produce more offspring and contribute more of their genes to the next generation • This results in a change in the gene composition from one generation to the next, with favorable (adaptive) characteristics accumulating over time o This change in the gene composition of a population over time is evolution in its most basic form Genetic variation is required for evolution by natural selection because if all organisms had the same genes and, as result, were completely similar, none of the organisms would be better suited for their environment than the others. As result, they wouldn’t have a reproductive advantage and their genes wouldn't be “selected” for in the population. All members of the population should survive and reproduce equally well. (Hardy-Weinberg equilibrium) 7. Lamarck thought that evolution was the best explanation for life’s diversity, as did Darwin. How did Darwin’s view differ from Lamarck’s? Lamarck • Said that species evolve by gradually
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