We present an active way to use a computer animation in secondary molecular genetics class. For this purpose we developed an activity booklet that helps students to work interactively with a computer animation which deals with abstract concepts and processes in molecular biology. The achievements of the experimental group were compared with those of a control group by means of a written questionnaire, which the students received right after the molecular genetics instruction. Analysis of the post-test showed that the mean score of the experimental group was significantly higher than the mean score of the control group. This positive trend was also reflected in personal interviews.