exam 1 key - BIOLOGY 325H Exam 1 Spring 2008 NAME_KEY Page 1 1[15 pts A Georges Cuvier showed that deeper strata of rock had creatures that differed

BIOLOGY 325H NAME _______ KEY _________________ Exam 1 Spring 2008 Page 1 1. [15 pts.] A. Georges Cuvier showed that deeper strata of rock had creatures that differed more from present day creatures than shallower strata. How does this evidence support evolution? Since deeper strata are usually older than shallower strata (newer sediment is deposited on older sediment), the fact that creatures in deeper/older strata are less similar to present day creatures than creatures found in shallower/younger strata supports the idea that organisms have evolved over time gradually changing until they became the species we see today. B. Explain how evolution by natural selection takes place, and do it in purely mechanistic terms. Do not use any language that suggests any intentionality in the process. A population must have genetically based variation (heritable variation) for some trait. Then because there are limited resources available in the environment, e.g., food, nesting sites, water, nutrients, etc., and because organisms nearly always produce more offspring than the environment can support, the offspring that have the best phenotype for the environment in which they live are more likely to survive to adulthood and may also produce more offspring. Thus in the next generation, the genes that produced the favored traits in the previous generation will increase in frequency in the population due to those individuals having more offspring relative to the individuals with the phenotypes that survived and reproduced at a lower rate. C. Why is it necessary to distinguish sexual selection from natural selection? Sexual selection differs from natural selection because it affects the traits of one sex more than the other, e.g., secondary sexual characteristics such as color in many species of male birds. In addition, sexual selection and natural selection can sometimes act in opposite directions, such as the example of the tail feathers in the widow birds. Sexual selection favored longer feathers, whereas natural selection favored shorter feathers. 2 . [15 pts.] Yucca is a succulent plant native to Texas, and entomologist Carmen Elytra studies a beetle species that lives on this plant. Yucca beetles with a homozygous recessive yy genotype are green in color, while the genotypes YY and Yy result in a blue color. Carmen observes that the green beetles are 5 times more likely to be eaten by birds when located on blue yucca, and that blue beetles are 5 times more likely to be eaten by birds when located on green yucca. Carmen releases equal numbers of green and blue beetles in two experimental gardens: one garden contains only green yucca; the other garden contains only blue yucca. A. Assume natural selection is the only factor that affects allele frequency in these two populations. Describe the expected change(s) in the frequency of the Y and y alleles over subsequent generations in each of the two gardens.