Modes of selection

Question 1

A population’s niche was displaced due to a tropical storm. Would you expect the intermediate or the extreme phenotypes to survive?

Answer 1

Extremes. Directional selection.

Question 2

What mode(s) of selection would be best in order to increase genetic variance?

Answer 2

Disruptive or sexual

Question 3

Guppies (a type of fish) that live in streams free of predators are larger than guppies that live in streams with predators. What is the mode of selection?

Answer 3

Directional

Question 4

Choose the type of selection described. Strong river currents uproot many aquatic plants. The strongest and weakest plants die.

Answer 4

Stabilizing

Question 5

Choose the type of selection described. A tornado hits a bird niche. Only birds that are heterozygous for the long wing gene (Ww) die.

Answer 5

Disruptive.

Question 6

Choose the type of selection described. In southern elk populations, only elks with the strongest and biggest horns mate to produce viable offspring.

Answer 6

Sexual (females choose strongest males)

Question 7

In generation after generation, individuals of the fly Drosophila were selectively bred. When flies with a strong tendency to fly toward light (positive phototropism) were used as parents for the next generation, their offspring had a greater tendency to fly toward light. Which mode of selection is this?

Answer 7

Directional

Question 8

In a population of marine snails that live among tan rocks covered with white barnacles, the animals are either white (and thus camouflaged while near the barnacles) or tan (and thus hidden while on bare rock. The snails that are neither white or tan, or that lie against the opposite-colored background, are more often seen and eaten by predatory shorebirds. Which mode of selection is this?

Answer 8

Disruptive

Question 9

Fossil evidence indicates that the average size of black bears in Europe increased with each glacial period of the ice ages. Which mode of selection is this?

Answer 9

Directional