Testing for the presence of a partially penetrant dominant gene

Favor, in the Appendix to a paper by Ehling and his collaborators (Ehling et al., 1982), develops a method that tests for the presence of a partially penetrant dominant cataract mutation in a suspected parent (showing lens opacity) outcrossed to a homozygous strain-101 mouse when no individual with lens opacity is observed in the progeny. This method, based on the Chi-square distribution, is examined as to the validity of the Normal approximation. An alternative procedure is discussed.