The utility of incompletely linked, selectively neutral, multiallelic markers for tracing the transmission of associated genes is examined theoretically for all genetic counseling situations in which the diagnosis of deleterious progeny is in question. The analysis focuses on the fraction of progeny from each two locus mating which can be diagnosed with minimal accuracy A solely on the basis of the marker alleles transmitted, as a function of A, the recombination fraction between the loci, and the gametic frequency distribution in the population. Together the results allow a quantitative assessment of the diagnostic value of a given marker-target locus association to the total population of at-risk individuals.