An individual with a disease demonstrates a set phenotypic presentation, Another individual with the same phenotypic presentation is discovered. When we sequence their genome, we find that there are two distinct DNA sequences involved, both differing from wt, but they are located in the same gene in both individuals. This demonstrates what? a) Allelic heterogeneity b) Locus heterogeneity c) Pleitropy d) Penetrance e) Expressivity