GRQ#22

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Apr 3, 2024

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L22: GRQs for How Populations Evolve II Chapter 13.12- 13.18 Reading objectives: ● Define genetic drift and how it affects small populations ● Describe and compare/contrast five different forms of natural selection by defining, giving examples, and drawing representative graphs. Read modules 13.12-13.18 1. When a population goes from large to small, genetic drift is more pronounced in the small population. What are two major reasons that populations go from large to small? 1) Bottleneck effect : Genetic drift resulting from a drastic reduction in population size; typically, the surviving population is no longer genetically represented of the original population. 2) Founder effect : Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool is not reflective of that of the original population. 2. Describe gene flow and give at least one example of it that you understand. Gene flow : the transfer of alleles from one population to another as a result of the movement of individuals or their gametes. ex . Humans today move more freely about the world than in the past, and gene flow has become an important agent of microevolutionary change in previously isolated human populations. 3. Natural selection is the only mechanism that consistently leads to adaptive evolution. For each of the FIVE types of natural selection, a) define it, b) give at least one example of it that will help you understand and remember it c) draw a graph if appropriate a. Directional selection : natural selection in which individuals at one end of the phenotypic range survive and reproduce more successfully than do other individuals ex . In a population of cliff swallows, birds with larger bodies survived an unusual period of cold weather. b. Stabilizing Selection : natural selection that favors intermediate variants by acting against extreme phenotypes ex . Birth weights of human babies are in the range of 6 to 8 pounds. Babies who are either much smaller or much larger are less likely to survive. c. Disruptive Selection : natural selection in which individuals on both extremes of a phenotypic range are favored over intermediate phenotypes ex . Young African black-bellied finches with small beaks, which feed mainly on soft seeds, and those with large beaks, which feed mainly on hard seeds, are more likely to survive than those with medium-sized beaks. d. Sexual Selection : a form of natural selection in which individuals with certain inherited traits are more likely than other individuals to obtain mates

ex . This distinction in appearance, called sexual dimorphism, is often manifested in a size difference, but it can also include forms of adornment, such as manes on lions or colorful plumage on birds. e. Balancing Selection : natural selection that maintains stable frequencies of two or more phenotypic forms in a population ex . If there are a lot of blue lizards, orange become more successful. Blue frequency drops. If there are a lot of orange lizards, yellow become more successful. Orange frequency drops. If there are a lot of yellow lizards, blue become more successful. Yellow frequency drops. - Heterozygote advantage : greater reproductive success of heterozygous individuals compared with homozygotes; tends to preserve variation in gene pools 4. True or False? ● New alleles arise as organisms need them. False ● Evolution leads to organisms perfectly adapted to their environments. False ● Evolution builds upon and modifies ancestral forms. True

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