IMAT 2013 Q42 [Population Phenotypes]

The increase in the frequency of one phenotype in a wild population of fish could be due to:

  1. an advantageous mutation.
  2. increased reproductive success of individuals with that phenotype.
  3. a change in the environment.

A. 3 only
B. 1 and 2 only
C. 1, 2 and 3
D. 2 and 3 only
E. 1 only

The answer to this question is choice C.

This is basically the concept of natural selection, where there are changes in the phenotype of a certain population in accordance to adaptation for the success of future generations. WIth that being said, let us then analyze the choices that were given.

  1. “An advantageous mutation”: Mutations are a product of alterations related to the DNA sequences of organisms. They can be sporadic or inherited, and in this case, inherited mutations will continue on if the product of the mutation itself helps the organism survive. It would follow logically that, since the organism is alive long enough to make offspring, these offspring will inherit this mutation, given its advantages for reproduction and survival. Thus, this statement can be included as a correct answer.

  2. “Increased reproductive success of individuals with that phenotype”: If a certain phenotype is present in an organism that is able to live long enough to reproductive age, it would make sense that this frequency of this phenotype will then increase given that it can be passed on to offspring. However, do not be confused with statement #1. In statement #1, the phenotype is in direct contribution to advantages that lead to longer survival, thus increasing the probability that the phenotype will be passed on in the first place. But in this statement, what is being implied is that a certain phenotype is present in an organism that has reproductive success. Which means that along with this reproductive success, is the concomitant passing down of that certain phenotype to the offspring.

  3. “A change in the environment”: The environment of the population plays a significant role in natural selection. For a population to survive as a whole, it must be able to adapt and withstand external factors, and ensure that future generations will be able to sustain themselves under the environment’s condition. This can include factors like access to food, predators, temperature, pressure, and even salinity. Thus, it would make sense that a certain phenotype that helps the population and its individuals to survive particular external conditions will increase in frequency since simultaneously, reproductive success will increase.

Thus, all statements are correct, making choice C as the correct answer.