Final answer:
The frequency of allele D in a population with two alleles, d and D, can be calculated by subtracting the frequency of allele d from 1. In this case, fD = 1 - fd = 1 - 0.6 = 0.4.
Step-by-step explanation:
In the given question, the population has two alleles, d and D, with a frequency of d (fd) equal to 0.6. Since these are the only two alleles in the population, the sum of their frequencies should add up to 1. Therefore, the frequency of allele D can be calculated by subtracting the frequency of allele d from 1.
Frequency of allele D (fD) = 1 - fd = 1 - 0.6 = 0.4.
Therefore, the correct answer is
option a) fD = 0.4
.