Almost half of blue-eyed, white cats are deaf. If blue-eyes and white fur provid

Question

Almost half of blue-eyed, white cats are deaf. If blue-eyes and white fur provide fitness advantages to cats, what is natural selection likely to result in? Select one: O a. All three traits (blue eyes, white fur, deafness) will decrease in the population due to disruptive selection b. Blue eyes and white fur will not increase in the population because of countervailing selection c. All three traits (blue eyes, white fur, deafness) will increase in the population due to directional selection d. The blue-eyed trait and the white fur trait will disappear or almost disappear e. Deafness will disappear

Explanation / Answer

The gene responsible for white fur in cats is an autosomal dominant gene denoted by W. This gene is pleiotropic, which means, being responsible for the white coat colour means it has a strong influence on blue eyes and deafness. The gene has complete penetrance for white coat colour (all cats that carry the gene will have a white coat), but it has incomplete penetrance for blue eye colour and for deafness (but these two are strongly linked). Thus, deafness is strongly linked to the white coat colour and blue eye colour, but not all white cats or white cats with blue eyes are necessarily deaf.

In the question, it has been mentioned that there is a certain level of fitness advantage in cats with white coats and blue eyes. So on one hand, we have a fitness advantage and on other we have deafness which is a negative character for survival. these two contradicting characters result in countervailing selection. Countervailing selection is where one cause of directional selection is usually counterbalanced by another.

From above we can conclude that correct answer is option 'b'.

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