Question

An organism has two different possible traits, A and B. A graph of the population is shown right. Which of the following statements is true about Trait B? Check all that apply.
It decreased in frequency over time.


It became extinct.


It is carried on a recessive allele.

Answer 1

The correct answer is: It decreased in frequency over time

From this graph, we can see that the trait B decreased in population over time.

Observable trait in population is called phenotype and it has its genetic component (genotype) that determinates it, but it also has environmental component (influence of environmental factors). So, change in frequency of the trait can be due to genetic or environmental changes.

Answer 2

Trait B is gradually decreasing over time mainly due to natural selection and natural selection can cause microevolution (change in allele frequencies), with alleles which are most suitable for environment to become more common in the population and if it continues to happen alleles not suited to the environment with respect to survival and reproduction can become extinct.

It is true that recessive trait is less common than dominant trait but if a trait is decreasing over time it does not necessarily means that it is due to its recessive allele because it could be possible that a recessive trait is more suited to the environment, so it will continue to survive and increase.

Natural selection is a mechanism of evolution, it's the only one that can consistently make populations adapted, or better-suited for their environment, over time.