Question

1. When comparing a range of viral populations in a particular year what characteristic is most associated with survival of the population to the next year.

A) a high rate of change in sequences at antigenic sites

B) a high rate of change in sequences generally

C) movement to a new host

D) ability to overwhelm the immune system

E) a low mutation rate

2. Some sharks migrate from the ocean to live in a freshwater lake. After a few generations scientists sequence an enzyme involved with moving ions across cell membranes in both the ancestral ocean population and the lake population. After correcting for the number of possible changes they found 3.3 nonsynonymous changes in the sequence for every synonymous change. This is evidence for which of the following?

A)No selection on the enzyme

B)Positive (directional) selection on the enzyme

C)Negative (stabilizing) selection on the enzyme

D)Ambiguous (disruptive) selection on the enzyme

3. Which evolutionary forces will tend to cause populations to diverge from one another genetically when they (the populations) are geographically isolated?

A) mutation, drift, selection

B) mutation, drift, migration

C) migration, drift, mutation

D) migration, selection

E) migration, selection, drift

Answer 1

1. A) a high rate of change in sequences at antigenic sites (this would ensure that the bacteria keeps changing the proteins and structures which are recognized by the host immune system. If the immune system fails to recognize the mutated antigenic sites, they will fail to mount an immune response against it and the bacteria will survive in the host. A high mutation rate is needed, movement to a new host doesn't necessarily mean that virus will survive in the new host.)

2. B)Positive (directional) selection on the enzyme (directional selection causes two traits to be eventually fixed in the population, one for saltwater and another for freshwater. Here no one trait is selected, hence no stabilising selection taking place. Disruptive selection would have occurred if there was a sudden change in environment forcing them to adapt to it.)

3. A) mutation, drift, selection (mutation will change the allele frequencies, genetic drift will also change the allele composition of the separated population, differential natural selection in different geographical locations will also make the population dissimilar from each other. Here migration will help in genetic intermixing, preventing them to diverge from eace other.)