In a hypothetical species of butterfly, wing spots are controlled by a single lo

ID: 274091 • Letter: I

Question

In a hypothetical species of butterfly, wing spots are controlled by a single locus where BB individuals have blue spots, YY individuals have yellow spots, and BY individuals have green spots. Ten years ago, a previous collector randomly collected 1000 butterflies and reported finding 90 blues, 420 greens, and 490 yellows. You collect 40 blues, 320 greens, and 640 yellows. Has there been evolution in this population? If yes, is natural selection involved? Explain and justify your answers. Please give me specific answer.

Explanation / Answer

The above example can be considered as a case for evolution. In this case, it is the natural selection of Y allele over B allele.

A brief analysis of the numbers given in the problem statement reveals the following –

Numbers of butterflies with respective phenotype

Change

10 years ago

Present

BB (Blue spots)

Decrease in population by 55.55%

YY (Yellow spots)

490

640

Increase in population by 30.61%

BY (Green spots)

420

320

Decrease in population by 23.81%

The numbers reveal that the frequency of ‘B’ allele in the population has decrease, whereas, the frequency of ‘Y’ allele in population has increased. This can be taken as a case where natural selection is favouring those individuals which contain the ‘Y’ allele over the ‘B’ allele.

Natural selection works by removing or eliminating those genetic variants that are less fit variants out of a population. It can be assumed that having blue spots rendered a disadvantage to the individuals, perhaps making them more susceptible to preying or mating incompatibility, whereas, the opposite could be true for those individuals having yellow spots. The fact that blue allele has not been completely eliminated yet could be attributed to the heterozygotic factor, where green individuals are carrying both ‘B’ and ‘Y’. Other reasons may include natural selection not having enough time to remove it, or the ‘B’ allele may not be reducing fitness until late in life.