I have conducted a lab with my IB Biology 11 class, regarding changes in allele frequencies within generations overseeing the natural selection of an advantageous phenotype. We were looking to conclude some sort of link between the changing allele frequencies and an overall changing population number of the species. Lab results saw, that as the frequency of the advantageous phenotype increased, the total population dipped and then increased after the 3rd generation. Can anyone point out any possible reasons as to why this occurred - regarding any factors at all? The image below depicts frequency of the advantageous allele vs total population.