To solve this problem, we need to use the Hardy-Weinberg principle, which provides a mathematical model to study genetic variation in a population under equilibrium.$\newline$According to the Hardy-Weinberg principle, the sum of the frequencies of all alleles in a population is 1. If the frequency of allele A is $p$ and the frequency of allele a is $q,$ then:$\newline p + q = 1 \newline$Given that the frequency of the dominant allele A is $0.4,$ we have:$\newline p = 0.4 \newline$Therefore, the frequency of the recessive allele a is:$\newline q = 1 - p = 1 - 0.4 = 0.6 \newline$The frequencies of the genotypes can be calculated as follows:$\newline \bullet$Frequency of homozygous dominant individuals (AA) is $p^2 = (0.4)^2 = 0.16 \newline \bullet$Frequency of heterozygous individuals (Aa) is $2pq = 2(0.4)(0.6) = 0.48 \newline \bullet$Frequency of homozygous recessive individuals (aa) is $q^2 = (0.6)^2 = 0.36 \newline$Therefore, the frequencies are:$\newline$0.16 (AA); 0.48 (Aa); 0.36 (aa)$\newline$This corresponds to Option 3.