What mathematical relationship is used to determine if microevolution is occurring within a pop. of organisms?

Question

I was thinking about the Hardy-Weinberg equation but it seems that it can only be used for a population that is not evolving.

Answer 1

The Hardy-Weinberg equation can certainly be applied to evolving populations; it just won't make correct predictions.  Deviations from these predications are what demonstrate that the population is evolving.

If you track a particular population in the wild and use the Hardy-Weinberg equation, you will come up with a prediction for the allele and genotype frequencies for the next generation.  If you conduct a follow-up study of this generation, and the Hardy-Weinberg numbers don't match your observed numbers, then the population has evolved.

It's sort of like the Ideal Gas Law from chemistry.  Real life gases don't behave like ideal gases, but the Ideal Gas Law is still a useful tool to make predictions and demonstrate properties of real gases.  The Hardy-Weinberg equation explains what happens in an ideal population that doesn't evolve so that properties of real life populations that do evolve can be illustrated.