A functional gene is present on one chromosome, a non-functional gene on the other.
Alleles segregate independently yielding four possible allelic combinations in gametes.
All the diagrams shown are simplified models. I. The result of this is that, in reality, all gametes will be different. Cross an avirulent pathogen strain with a virulent pathogen strain. Examine distribution of phenotypes in progeny population. Cross a resistant host with a susceptible host.