Incorporation of active learning into large lecture classes is gaining popularity as a pedagogical method due to its known benefits in helping learning outcomes. A more recent active learning technique that has emerged is the flipped classroom. In this study, we investigated the effects of incorporating a "partial-flip" into an introductory general biology course, where only a portion of the class time was spent in a flipped classroom format. This partial flip presented the classic biology experiment of Meselson and Stahl that discovered the mechanism of DNA replication. Performance on in-class formative assessments and subsequent summative assessments (eg out-of-class assignments and exams relating to this material) was compared between a class that had the partial flip and a control class that had a traditional lecture. The partial flip students scored higher on in-class formative questions, specific exam questions and final exam essay questions. We found that the partial flip had different effects in males versus females depending on the assessment. The partial flip manipulation appeared equally effective in aiding both below and above average students in formative assessments. Overall, this study shows that the partial flip classroom can be an effective technique to incorporate into existing courses and that it does provide some benefits compared to traditional lecture.