Disease and Natural Selection
One type of natural selection is called frequency-dependent selection. This type of selection favors phenotypes that are either common, positive frequency-dependent selection. or rare, negative frequency-dependent selection. An example of negative frequency-dependent selection can be observed in the interaction between the human immune system and various infectious agents such as bacteria or viruses. As a human population is infected by a common strain of bacteria or virus, the majority of individuals in the population become immune to it, either naturally or through the use of antibiotics and/or vaccinations. This then selects for rarer strains of the bacteria or virus. which can still infect the population because of mutations. The new strains have greater evolutionary fitness because they are less common.
Question 1
Consider the model of bacterial resistance to antibiotics. Use the Roman numerals (I - III) to guide you through the steps, describe how a scientists would explain how natural selection contributes to antibiotic resistance.
Responses
A There is a change in the environment when an antibiotic is added. Some of the bacteria adapt to the new environment. They survive and reproduce.There is a change in the environment when an antibiotic is added. Some of the bacteria adapt to the new environment. They survive and reproduce.
B In any population variation exists. Most bacteria die when exposed to an antibiotic but some survive because they are resistant. They survive and reproduce.In any population variation exists. Most bacteria die when exposed to an antibiotic but some survive because they are resistant. They survive and reproduce.
C In a population of bacteria that are exposed to antibiotics some bacteria are able to change their genetic make-up and survive. The new genotype is passed on to offspring.In a population of bacteria that are exposed to antibiotics some bacteria are able to change their genetic make-up and survive. The new genotype is passed on to offspring.
D Sexual reproduction of bacteria cause variations. Some bacteria survive antibiotics and some do not. Eventually because of sexual reproduction over time all of the bacteria will become extinct.Sexual reproduction of bacteria cause variations. Some bacteria survive antibiotics and some do not. Eventually because of sexual reproduction over time all of the bacteria will become extinct.
Question 2
The CDC recommends a yearly flu vaccine as the most important step in protecting against influenza and its potentially serious complications. The seasonal flu vaccine protects against the three or four influenza viruses that research indicates will be most common during the upcoming season. If you do get a flu shot, you can still possibly get the flu. Using the illustration and prompt, explain how this can happen. All BUT ONE choice could apply.
Responses
A Variation in the influenza virus population always exists.Variation in the influenza virus population always exists.
B The influenza virus mutates rapidly, from season to season.The influenza virus mutates rapidly, from season to season.
C Once subjected to the vaccine, the virus begins to evolve and become resistant.Once subjected to the vaccine, the virus begins to evolve and become resistant.
D You are exposed to an influenza virus that was not included in the seasonal vaccine.
1 answer