How would you tell if a population is at Hardy-Weinberg equilibrium?

Answer 1

If there is no change in the population over time.

So I'm staying if dP/dt = 0 you are at equilibrium.

Good Luck!

Answer 2

In a practical sense - you can't for most natural populations. To do so would require knowledge of all the alleles present in a population, the ability to recognize the different genotypes, and a sufficient sample of the population to calculate the allele frequencies. In practice this is sometimes done for a particular group of alleles that have recognizable phenotypes, so you can just count the phenotypic frequencies and compare them to expected frequencies under all of the Hardy-Weinberg assumptions. Using phenotypes, you still would not know for sure if the allele frequencies met Hardy-Weinberg, because the recessive traits are masked. But you can at least tell if phenotypic frequencies are consistent.