The Framework for Science Education and the Next Generation Science Standards in the USA emphasize learning progressions (LPs) that support conceptual coherence and the gradual building of knowledge over time. In the domain of genetics there are two independently developed alternative LPs. In essence, the difference between the two progressions hinges on conjectures regarding the accessibility of Mendelian versus molecular genetics, the conceptual dependencies between them, and the order in which they should be taught. The discrepancies between the two progressions stem, in part, from gaps in the current research base. To address the question of whether learning one aspect of genetics, Mendelian or molecular, supports the learning of the other, we analyzed correlations between students' test scores on item subsets for Mendelian and molecular genetics on written pre-post assessments. Students were seventh graders who received intensive instruction in Mendelian and molecular genetics. We found that students' pretest scores on the molecular items were moderately correlated with their posttest scores on the Mendelian genetics item set (but not the other way around). This suggests that molecular genetics understandings may bootstrap the learning of Mendelian genetics. Implying that, in contrast to prevalent practice, molecular genetics should be taught before Mendelian genetics.