Worksheet 17.2: Evolution as Genetic Change in Populations (pages ; ibooks pages )

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1 Worksheet 17.2: Evolution as Genetic Change in Populations (pages ; ibooks pages ) 1. If a trait made an organism less likely to survive and reproduce, what would happen to the allele for that trait? 2. If a trait had no effect on an organism s fitness, what would likely happen to the allele for that trait? Use the table showing the evolution of a population of mice to answer Questions 3 5. Initial Population Generation 10 Generation 20 Generation 30 90% 80% 70% Black 40% Black Black Black 10% Brown 20% Brown 30% Brown 60% Brown 3. Is the trait for fur color a single-gene trait or a polygenic trait? Explain your answer. 4. Describe how the relative frequency of fur color alleles is changing in this population and propose one explanation for this change. 1

2 5. Suppose a mutation causes a white fur phenotype to emerge in the population. What might happen to the mouse population after 40 generations? 6. What effect does stabilizing selection have on variation in a population? For Questions 7 9, match the type of selection with the correct situation. Type of Selection! 7. Directional! 8. Stabilizing! 9. Disruptive Situation A. Individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle. B. Individuals at one end of the curve have higher fitness than individuals in the middle or at the other end. C. Individuals near the center of the curve have higher fitness than individuals at either end. 10. Draw the missing line in the graph on the right to show how disruptive selection affects beak size. For Questions 11 13, complete each statement by writing the correct word or words. 11. In small populations, random changes in! is called genetic drift. 2

3 12. A situation in which allele frequencies change as a result of the migration of a small subgroup of a population is known as the!. 13. The! is a change in allele frequency following a dramatic reduction in the size of a population. 14. In most populations, a trait that has higher fitness leads to greater numbers of organisms with that trait. On the graphs below, dotted lines show the original population. The solid lines show the population after selection has taken place.!! Follow the directions:!!!! Label the graph that shows stabilizing selection.!!! Label the graph that shows disruptive selection. Percentage of Human Population original population!!!!!! Number of Birds in Population original population Birth Weight Beak Size Answer the questions.!!! 15. With which type of selection do organisms in the middle of the curve have the highest! fitness?! 16. In disruptive selection, organisms on which part of the curve have the lowest fitness?! 3

4 17. How does the curve change in stabilizing selection? A. The curve becomes shorter and wider. B. The curve becomes taller and narrower. C. The curve moves to the right. 18. The plants in an area have either very small or very large seeds. Birds with small beaks can eat small seeds, and birds with large beaks can eat large seeds. Birds with smaller beaks and birds with larger beaks become more common than birds with medium beaks. What type of selection is this? A. stabilizing selection B. disruptive selection C. directional selection The Hardy-Weinberg Principle Genetic equilibrium occurs when the allele frequencies in a population remain the same. If the allele frequencies do not change, the population will not evolve. The Hardy-Weinberg principle lists the five conditions in which evolution does not occur in a population. 19. Read the chart below. Use phrases in the word box to identify each condition that leads to genetic equilibrium. The first row has been completed for you. large population no natural selection no movement random mating no mutations The Hardy-Weinberg Principle large population The more individuals in the population, the smaller the effect of genetic drift. No changes to genes means new alleles are not introduced into the population s gene pool. Each individual in a population has the same chance of passing on its alleles. No new alleles are introduced into the population s gene pool by new individuals. No phenotype can have a selective advantage over another all individuals have equal fitness. 4

5 Read the descriptions below. Use what you know about the Hardy-Weinberg principle to identify what is happening. 20. Genetic drift strongly affects the population. A. small population B. random mating C. no movement into or out of the population D. no natural selection 21. Lions with a darker fur color have the same chance to reproduce as lions with a lighter fur color. A. large population! C. random mating B. no mutations! D. no natural selection 22. Fitness is basically the same among individuals in the population. A. large population! C. random mating B. no mutations! D. no natural selection 23. Complete the concept map about Genetic Drift 5