Question

The fruit fly Drosophila melanogaster has an allele that confers resistance to DDT and similar insecticides. Laboratory strains of D. melanogaster have been established from flies collected in the wild in the 1930s (before the widespread use of insecticides) and the 1960s (after 20 years of DDT use). Lab strains established in the 1930s have no alleles for DDT resistance. In lab strains established in the 1960s, the frequency of the DDT-resistance allele is 37%. Which statement is correct?

A) Alleles for DDT resistance arose by mutation during the period of DDT use because of selection for pesticide resistance.
B) The evolutionary fitness associated with the heritable trait of DDT resistance changed once DDT use became widespread.
C) Resistance to DDT evolved in some fruit flies in order to allow them to survive.

Answer 1

The answer is option "B"

Step-by-step explanation:

DNA is comprised of a set of genes that dictates a given trait. The genes themselves are comprised of alleles that allow for variations and differences in the trait that the concerned gene is responsible for. In the case of D. Melanogaster, there is an allele that allows for resistance to pesticides such as DDT. The two samples that are referred to in the question are differentiated on the basis of the amount of time that has lapsed since the start of significant DDT usage. So at the time when widespread DDT usage was not in place, the sample showed no DDT resistant alleles. With the passage of time in which DDT usage grew, the resultant effect as evidenced from the later sample indicated a significantly higher percentage of DDT resistant allele. This means that the ability of this species of fruit flies to survive, referred to as their evolutionary fitness, increased only after use of DDT increased. This means that DDT resistance trait changed as a natural response to the introduction of a different climate thereby allowing subsequent offspring of fruit flies to boast of higher numbers of alleles that have DDT resistance capacities thus allowing them to survive.