Dependence of the minimal size of a pedigree sample providing the given quality of a linkage decision on the genotype penetrance of the localized gene is considered. The two ways of the sample informativity increase are discussed and their effects are estimated. These ways are: the adequate choice of a marker gene and certain complication of a pedigree structure. It is shown for the latter that the effect can be achieved only for certain phenotypic characteristics of the additional pedigree members.