When a population is at Hardy-Weinberg equilibrium which one of the following is true?

a. Genotypic frequencies change generation after generation.
b. Allele frequencies change generation after generation.
c. The population is a sink for immigrants.
d. One can calculate the recessive allele frequency directly from the homozygous recessive genotype.
Individuals of like genotype are most likely to mate.

The Hardy-Weinberg principle was given by two different scientists Godfrey Hardy and the Wilhelm Weinberg which worked on understanding the population genetics.

The Hardy- Weinberg equilibrium is based on certain assumptions like population should have no mutations, no emigration, no selective pressure, no migration and the population should be infinite.

Since the Hardy- Weinberg equilibrium is widely used to determine the allelic frequency from the genotype therefore option-D is the correct answer.