This study investigated the retention of meaningful understanding of the biological topics of meiosis, the Punnett square method and the relations between these two topics. This study also explored the predictive influence of students' general tendency to learn meaningfully or by rote (meaningful learning orientation), prior knowledge of meiosis, instructional treatment (students told relations between concepts, students asked to construct relations themselves) and all interactions of these variables on the retention of meaningful understanding of the topics. A 50-item Likert instrument taken by the students and teacher ratings of their students' approach to learning (meaningful, rote) were used in combination as a measure of students' meaningful learning orientation. The mental model technique was used to assess students' meaningful-level and rote-level understandings of the topics. Students were given a pre-test mental model on meiosis (prior knowledge variable) and were randomly assigned to the two instructional treatments. Results of correlations indicated that students' attainment of meaningful understanding as measured immediately after instruction was significantly and positively related with their retention of meaningful understanding. Stepwise multiple regressions revealed that students' retention of meaningful understanding of meiosis was predicted by student's meaningful learning orientation and prior knowledge of meiosis. The interactions of meiosis and meaningful learning orientation best predicted both student' retention of meiosis and the conceptual relation between the topics. None of the predictor variables (prior knowledge, meaningful learning orientation, and treatment) nor the interaction terms predicted students' retention of meaningful understanding of the Punnett square method. (Author/PR)