Characteristics of successful and unsuccessful problem solvers in categorization tasks are examined in this study of undergraduate students. Findings are reviewed of the categorization and solution tasks undertaken by a group (N=21) of science majors at a private university. The subjects were classified as either successful or unsuccessful in their efforts as problem solvers with classical genetics tasks. It was found that having a mental framework for categorizing problems according to similarities in the way they can be solved contributed to problem-solving success. It was suggested that successful genetics probelm solving involves not only the ability to recognize the genetics concept underlying the problem, but also the ability to recognize the appropriate approach to solving the problem. Detailed tables summarize the data from the study. (ML)