Explanation

According to Hardy-Weinberg law, at equilibrium, genetic and allelic frequencies remain constant from one generation to next generation. It can be mathematically expressed as For allelic frequency A+a=1 For genetic frequency $A^{2} + a^{2} + 2Aa = 1$ So, allelic frequency of A=0.7 So, allelic frequency of a=1$-$0.7=0.3 Therefore, the genetic frequency of Aa is =2(Aa) $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 2(0.7 \times 0.3)$ $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = 2 \times 0.21 = 0.42$ So, frequency of Aa=0.42.