The shell of a particular species of snail exhibits anywhere from 3 to 10 coils when mature. Over a series of three years, a scientist counts the number of coils in the shells of all the mature individuals in a population of snails. Year after year, the most common phenotype is 7 coils. Snails with 3 coils or 10 coils are very rare. This is an example of _____ selection.
A)disruptive
B)stabilizing
C)directional
D)sexual

Question

Quizplus · Accepted Answer

Stabilizing selection occurs when the majority of individuals in a population have an intermediate phenotype, and extreme phenotypes are selected against. In this case, the most common phenotype is 7 coils, which suggests that individuals with 3 or 10 coils are selected against, leading to a stabilizing effect on the population. This is not an example of disruptive selection, which would favor extreme phenotypes, nor directional selection, which would result in a shift towards one extreme phenotype. There is also no evidence that this is an example of sexual selection, which occurs when individuals with certain traits are more likely to mate and pass on those traits to their offspring.

The Shell of a Particular Species of Snail Exhibits Anywhere