1. Some evolutionary biologists define a species as a "closed gene pool." Justify this description or criticize it on the basis of definitions given in the chapter for a "species" and "gene pool."

2. What is the difference between "frequency" and "probability"? How are these statistical expressions related to population genetics?

3. A hypothetical female theropod with a homozygous recessive gene for a reduced hallux mated with a male theropod with a heterozygous condition that has a normal-sized hallux as the dominant trait.

a. What was the probability of their offspring having the phenotype of a reduced hallux?

b. What is the probability for the next generation (the offspring of the offspring) having the phenotype of a reduced hallux?

c. What is the assumption of the preceding probabilities? In other words, what factors could change the expected gene frequencies?

Out of all of your friends, think about how representative one of them might be for the phenotype of Homo sapiens if he or she was randomly picked as a "type specimen."

CUSSION QUESTIONS Continued a. How much variation would your friend have in his or her living appearance?

b. Out of those observed variations, what inheritable features do you think would be evident in the fossil record that might define them as typical of your species?

c. What acquired features do you think would be unrepresentative of their genome and thus would be a source of confusion for paleontologists of the future (whatever their species might be)? For example, do they have dyed hair, tattoos, piercings, or other modifications?

5. Explain how the evolutionary development of a cledioic egg for amniotes could have occurred through the following models:

a. Allopatric speciation b. Sympatric speciation c. Phyletic gradualism d. Punctuated equilibrium e. Character displacement f. Red Queen

6. Based on the information presented in the chapter, make your own cladogram showing the ancestry of the following modern reptile groups: turtles, snakes, lizards, crocodiles, and alligators. Which pair among these five groups seems to be the most related and which pair seems the least related?

7. The overall average height of humans has increased in the past 1000 years, based on measurements of skeletons from that time span as well as data taken from living people. Is this increase in height an example of directional selection (Cope's Rule)? Why or why not?

8. Given the primitive dinosaur traits of bipedalism, think about the following:

a. How could natural selection have caused some descendants of the first dinosaurs, such as prosauropods, to go to quadrupedalism as a mode of locomotion?

b. What are some environmental factors that might have favored quadrupedal postures? What evidence in the geologic record would be needed to corroborate your hypotheses?

c. What are some possible intraspecific factors that might have caused sympatric speciation in such a direction? What evidence in the geologic record would be needed to corroborate your hypotheses?

9. Of the amniotes mentioned in the chapter, which ones did you mistakenly think were dinosaurs before reading this book? How would you go about convincing someone else that these animals were not dinosaurs?

10. How could a meteorite impact have caused problems for ecosystems during the Late Triassic? List some of the effects of an impact that are unlike the more gradual changes that might have been caused by continental rifting.

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