Limits of the general two-allele single locus model with incomplete penetrance

A graphical method is presented that allows an investigator to find the mathematical limits of the general one locus two allele genetic model for any trait whose population prevalence is known. It is seen that while the model is quite flexible in its ability to fit family data, there remains a large area where the model cannot be fitted. Specific sub-regions corresponding to particular hypotheses (e.g. underdominant v. intermediate v. overdominant) can be found, thereby limiting the area that needs to be searched by other more complicated techniques. Moreover, knowledge of where a set of observations lies can enable an investigator to frame and test specific subhypotheses.