Why is it important that P + Q always equals 1 in the Hardy-Weinberg equation?

The reason P + Q must always equal 1 in the Hardy-Weinberg equation is that this equation represents the total allele frequency in a population for a given trait. In this context, P represents the frequency of one allele (typically the dominant allele), while Q represents the frequency of the other allele (usually the recessive allele) for a specific gene. Since these two alleles make up all the allele options available for that gene within the population, their combined frequencies must sum to 1, or 100%.

This relationship is fundamental in population genetics as it allows researchers to understand the genetic structure of a population and assess whether it is in a state of equilibrium or whether evolutionary forces are acting upon it. By confirming that the sum of the allele frequencies equals 1, it underscores the principle that any changes in allele frequencies over generations would indicate some form of evolution, whether through natural selection, genetic drift, mutation, or gene flow.