Question

the distribution of shell heights in a population of snails changed over time, as shown.
distribution of shell heights
initial
final
which of the following best explains what happened to the genetic diversity of this snail population in regard to shell height?
1 genetic diversity decreased because of selection pressure.
2 genetic diversity increased because of changes in food sources.
3 genetic diversity stayed the same because of equal birth and death rates.
4 genetic diversity increased because of the introduction of a new behavior.

Explanation:

Looking at the bar graphs, the initial distribution of shell heights is more spread out (has more variation in shell heights), while the final distribution is more concentrated around a central height. Selection pressure (like natural selection) can favor certain traits (shell heights here), reducing the variation in the population. So genetic diversity (which relates to trait variation) decreases. Option 2 says diversity increased, which contradicts the graph. Option 3 says it stayed same, but the graph shows a change. Option 4 also says increased, which is wrong. So option 1 is correct.

Answer:

1. Genetic diversity decreased because of selection pressure.