PROBLEM SET Qs for Exam 1

Question 1

Review the process by which the HIV population inside a human host evolves resistance to the drug AZT. What traits of HIV contribute to its rapid evolution? How might a similar scenario explain the evolution of antibiotic resistance in a population of bacteria?

Answer 1

The traits that contribute to rapid evolution of HIV: mutations occur rapidly as HIV has a high turnover rate, which leads to a larger population size within the host. Bacteria also proliferate quickly and at a fast rate, so more mutations accumulate with each replication, allowing for mutations that are potentially advantageous in resisting antibiotic treatment to arise.

Question 2

The idea behind multi-drug therapy for HIV is to increase the number of mutations required for resistance and thus reduce genetic variation in the viral population for survival in the presence of drugs. Could we achieve the same effect by using antiretroviral drugs in sequence instead of simultaneously?

Answer 2

No, it could lead to a more wide-spread resistance to drugs. The HIV population would only need to obtain one drug-resistance at a time. It is unlikely that HIV would accumulate multiple simultaneous mutations to survive the simultaneously administered drugs.

Question 3

Alexander Graham Bell wrote that “natural selection no longer influences mankind to any great extent” Agree? Evidence?

Answer 3

Disagree. Although, we do control the aspects of many things that could harm us, like creating vaccines to fight disease. But, an example that natural selection is still in effect is having immunity to a disease, or a genetic disease that is selected against if the individual doesn’t survive to produce offspring.

Question 4

Selection of different virus strains within one host and selection of those virus strains that are able to transmit themselves from host to host. Hypothesis: disease causing agents naturally evolve into more benign forms as the immune systems of their host evolve more efficient responses to them. Is the evidence we have reviewed on the evolution of HIV within and among hosts consistent with this hyp?

Answer 4

No, because HIV hasn’t been shown to evolve into the more benign form. HIV has shown the tendency to evolve into a stronger version of itself. The most virulent version of HIV is spread widely throughout the host.

Question 5

Idea: relationships btwn parasites and hosts inevitably evolve toward peaceful coexistence. Parasite population is likely to survive longer if it’s host remains unharmed. With HIV as an example, do you agree?

Answer 5

No consistent thoughts because HIV/viruses only need a living host long enough to spread to a new host, thus the survival of the previous host doesn’t matter. Some parasites do coexist with host, but then they’re not really parasites because the term implies that the host is harmed. A high-virulence parasite can also survive if it can transfer to another host before the other dies. Parasites tend to proliferate rapidly and have even evolved different mechanisms of transfer, like water or poop.

Question 6

HIV is a tiny, robotic, molecular machine. Under what conditions could robots actually evolve? Is it necessary that the robots reproduce, for example?

Answer 6

For entities/organisms to evolve, they must have varied genetics, reproduce and pass on those varied traits to offspring. It is necessary for the “robots” to somehow create mutations so that the offspring will have varied genetics that will select depending on how the environment affects the entity/organism.

Question 7

What was evidence for evolution for Darwin?

Answer 7

• -vestigial structures (structures that no longer serve a function that they once did–pelvic bones in snakes
• -Morphology between different sites-biogeography (evident in the different Iguanas on SA and Galapagos)
• -Geology (observing fossils and how long they took to form)

Question 8

How does the control strain support the interpretation that two-dozen generations of selective breeding had altered the experimental population? If Garland had simply compared the behavior of the first experimental generation, would the evidence for evolution be as strong?

Answer 8

The control strain of mice had the same wheel and same environment as the experimental mice. The control mice and their propensity to run on the wheel didn’t really change over time. In contrast, the experimental mice ran faster and evolved with every generation as those fast mice were being selected and bred for that drive-to-run trait. If he had just compared the behavior of the first experimental generation to the control population, nothing drastic would have changed, as evolution happens gradually. The experiment shows that the selective factor that was provided by Garland and colleagues is what drove evolution of the fast mice in a specific direction. Artificial selection allows for this to happen faster, but the results of this experiment show that it took 24 generations to conclude that selective breeding had in fact altered the experimental population.

Question 9

How does the single highly variable population of stickleback bear on the claim that the two forms in the lake are different species? How does it bear on the claim that varying degrees of divergence among stickleback populations provide enough evidence for speciation?

Answer 9

The two forms of stickleback that can’t mate prove that they are different species, despite having phenotypic similarities. Varying degrees of divergence among the stickleback populations provide evidence for speciation because somewhere along the line of similar species, some of them can actually breed. It just goes to show that even though there are polar species that cannot interbreed, they have relatives in the middle that could be able to.

Question 10

What else, besides aerodynamics, do feathers do for birds today? What advantages might feathers have offered for dinosaurs? Can you think of a way to test your hypothesis?

Answer 10

Feathers provide insulation for birds today, so this could have been beneficial for dinosaurs as reptiles, who are ectothermic. A way to test this could be to take a “modern day dinosaur” who is most closely related to dinosaurs, such as the crocodile, and place feathers or a feather blanket on the reptile and see how this affects its body temperature and perhaps how long it chooses to sunbathe to warm itself. This might give some insight as to how feathers could insulate reptiles and provide a way to stay warmer.

Question 11

What are Darwin’s 4 postulates?

Answer 11

• -Variation exists
• -variation is heritable
• -survival and reproduction are not equal
• -survival and reproduction are not random

Question 12

What would have happened in the snapdragon experiment if any if the four postulates had not been true?

Answer 12

All flowers would have been the same color and evolution in the sense of a variable population would not occur. All flowers would be equally attractive to pollinators. Some plants would have more bee visits than others, but it would not be due to color.

Question 13

If the 4 postulates are true for a population, is there any way that evolution cannot happen?

Answer 13

A population is certain to evolve, unless selection is really weak and genetic drift is strong. Evolution is always happening, but there is no set path. Natural selection is occuring in one way or another in populations today. We can make predictions, but we cannot conclude what the evolving populations consist of.

Question 14

What does this imply about whether evolution is or is not occurring in most populations today?

Answer 14

Since the 4 postulates are true, virtually all populations are mostly likely evolving today.

Question 15

Finch bill data demonstrating Darwin’s 4 postulates. What would the distribution look like if bill depth was not variable?

Answer 15

If bill depth was not variable, the distribution would show one tall bar representing all of the same bill depth.

Question 16

What would this distribution look like if bill depth was variable but the variation was not heritable?

Answer 16

If the depth was variable and the variation was not heritable, the post-drought birds would have the same bill depth as the pre-drought birds. The population as a whole would not evolve.

Question 17

Finch data. Why is the line drawn from 1978 data, after the drought, higher on the vertical axis than the line drawn from 1976 data, before the drought?

Answer 17

The trend is clearly that the thick-beak parents have thick-beak offspring, demonstrating the heritability of beak depth. The difference in the lines suggests that a part of the beak variation is not heritable. This was due to an environmental event that affected beak depth.

Question 18

How would you respond to the creationist’s criticism that a a little beak change in Darwin’s finches is just microevolution not macroevolution? Do you think the ongoing effort of the finch bill project has been worthwhile? Is it useful to try to document microevolution, and does it tell us anything about how macroevolution might work?

Answer 18

The changes in beak was not random in the sense that it was a result of response to the environment, in other words, variation in the environment leads to variation in the birds. Climate change predicted for galapagos: increase in temp and dryness→ prediction would be that the beaks would become bigger and stouter in response to this. I think that the ongoing effort of the finch bill project has been worthwhile. Because the galapagos finch population variation is such a perfect example demonstrating natural selection, it is important to witness this process as it is uniquely undisturbed by outside factors. What we can witness from microevolution allows us to look on a larger scale at macroevolution.

Question 19

Alabama School Board discussing evolution disclaimer: “No one was present when life first appeared on Earth; therefore, any statement about life’s origins should be considered as theory, not fact.” Do you accept the last sentence in this statement? Does the insert’s point of view pertain to other scientific theories, such as cell theory, the atomic theory, the theory of plate tectonics, and the germ theory of disease?

Answer 19

I do not agree because I think the way that a theory is described is incorrect, however, overall I do agree. A theory is the most solid form of conclusion/an answer to a scientific problem/inquiry. The insert makes it seem as though fact and theory are interchangeable, when there is so much evidence that goes into developing a scientific theory. The insert’s view isn’t completely in line with cell theory and other scientific theories because these theories are observable today. We cannot test the when life first appeared on earth, but we can collect a whole spectrum of scientific evidence to theorize when this was.