Credit Quiz 2 1) If two modern organisms are distantly related in an evolutionary sense, then one should expect that A) they live in very different habitats. B) they should share fewer homologous structures than two more closely related organisms. C) their chromosomes should be very similar. D) they shared a common ancestor relatively recently. E) they should be members of the same genus. 2) Within a few weeks of treatment with the drug 3TC, a patient’s HIV population consists entirely of 3TC-resistant viruses.
How can this result best be explained? A) HIV can change its surface proteins and resist vaccines. B) The patient must have become reinfected with 3TC-resistant viruses. C) HIV began making drug-resistant versions of reverse transcriptase in response to the drug. D) A few drug-resistant viruses were present at the start of treatment, and natural selection increased their frequency. E) The drug caused the HIV RNA to change. The graph in Figure 22. 3 depicts four possible patterns for the abundance of 3TC-resistant HIV within an infected human over time.
Figure 22. 3 3) If 3TC resistance is costly for HIV, then which plot (I—IV) best represents the response of a strain of 3TC-resistant HIV over time, if 3TC administration begins at the time indicated by the arrow? 4) A biologist studied a population of squirrels for 15 years. During that time, the population was never fewer than 30 squirrels and never more than 45. Her data showed that over half of the squirrels born did not survive to reproduce, because of competition for food and predation.
In a single generation, 90% of the squirrels that were born lived to reproduce, and the population increased to 80. Which inference(s) about this population might be true? A) The amount of available food may have increased. B) The number of predators may have decreased. C) The squirrels of subsequent generations should show greater levels of genetic variation than previous generations, because squirrels that would not have survived in the past will now survive. D) A and B only E) A, B, and C 5) Which of these is the smallest unit upon which natural selection directly acts?
A) a species’ gene frequency B) a population’s gene frequency C) an individual’s genome D) an individual’s genotype E) an individual’s phenotype 6) Which of these is the smallest unit that natural selection can change? A) a species’ gene frequency B) a population’s gene frequency C) an individual’s genome D) an individual’s genotype E) an individual’s phenotype In a hypothetical population of 1,000 people, tests of blood-type genes show that 160 have the genotype AA, 480 have the genotype AB, and 360 have the genotype BB. ) What is the frequency of the B allele? 8) If there are 4,000 children born to this generation, how many would be expected to have AB blood under the conditions of Hardy-Weinberg equilibrium? 9) In peas, a gene controls flower color such that R = purple and r = white. In an isolated pea patch, there are 36 purple-flowering plants and 64 white-flowering plants. Assuming Hardy-Weinberg equilibrium, what is the value of q for this population? 10) In a hypothetical situation, a certain species of flea feeds only on pronghorn antelopes.
In rangelands of the western United States, pronghorns and cattle often associate with one another. If some of these fleas develop a strong preference, instead, for cattle blood and mate only with fleas that, likewise, prefer cattle blood, then over time which of these should occur, if the host mammal can be considered as the fleas’ habitat? 1. reproductive isolation 2. sympatric speciation 3. habitat isolation 4. prezygotic barriers A) 1 only B) 2 and 3 C) 1, 2, and 3 D) 2, 3, and 4 E) 1 through 4