The purpose of this study was to investigate the relationship between the achievement of some abstract concepts in "molecular genetics" and prior knowledge, formal reasoning ability, and sex. The major findings of the study were: (1) prior knowledge had a high significant correlation with the achievement of abstract concepts; (2) the correlation between the formal reasoning and the achievement of abstract concepts was found to be relatively moderate, but significant; (3) sex was found to correlate significantly but low with the achievement of abstract concepts; (4) the variables succeeded in predicting the achievement of abstract concepts; and (5) a relatively high percentage of variability in the achievement of abstract concepts was accounted for by prior knowledge and formal reasoning. The major conclusions of this study are that the prior knowledge and formal reasoning play a major role in students' achievement of abstract concepts, and the effect of student's prior knowledge on this achievement seems to exceed that of formal reasoning. A 7-page list of references is included. (CW)