In this paper we discuss an activity through which students learn basic concepts in genetics by taking part in a police investigation game. The activity, which we have called Recal, immerses students in a scientific-based scenario in which they play a role of a scientific assessor. Players have to develop and use scientific reasoning and evidence-based decision-making to solve the given enigmas along the game. The activity aims to improve students' knowledge of genetics and show them how genetic evidence can be applied in forensic science. The activity (known as "the Recal case") uses a problem-based learning educational methodology. It is learner-centred and students play an active collaborative role. The methodology requires students to structure their knowledge, and develop their reasoning processes and self-directed learning skills. The activity has been developed for a range of audiences, including high school students, undergraduates engaged in pre-service teaching and adults of all ages. A case study has also been carried out with a group of 120 pre-service student teachers from the Universitat Rovira i Virgili (Tarragona, Spain) to check whether the coherence in the running of the game, whether its effectiveness as a learning activity and whether its dynamics and motivational aspects are acceptable.