This study compared the problem-solving performance of university genetics professors and genetics students, and therefore fits the expert versus novice paradigm. The subjects solved three genetic pedigree problems. Data were gathered using standard think-aloud protocol procedures. Although the experts did not differ from the novices in terms of the number of correct solutions obtained, there were significant differences favoring the experts in terms of the completeness and conclusiveness of the solutions. The experts identified more critical cues in the pedigrees which were used to generate and test hypotheses, they tested more hypotheses by assigning genotypes to individuals in the pedigrees, and were more rigorous than the novices in the falsification of alternative hypotheses. The experts varied their problem-solving strategy to suit the particular conditions of problems involving rare or common traits. Novices did nor recognize the need to make such modifications to their strategies.