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This article focuses on students’ discursive moves and reasoning practices while engaged in a task that requires making explanatory links between sickle cell disease and malaria. Both diseases pertain to key areas of the biology curriculum, namely, genetic variability and natural selection, and are connected to the theory of evolution of living organisms. Specifically, this study examines the intersections among rhetoric, argumentation and epistemic actions in supporting students’ understanding of complex biological dynamics, which are interlinked across time and space, but are often addressed separately in the curriculum. Data were collected over the course of two school years (2014–2016) with a group of 20 15–17-year-old students and their biology teacher. The findings indicate that while rhetorical moves helped students mobilize data, the use of evidence to support claims remained limited. Conversely, the type of epistemic actions enacted by the students appears to be directly related to the type of data being analysed. Hence, rhetorical moves in combination with argumentation practices appear to account for students’ differential performances in building more complex explanations of evolutionary topics. We conclude that further understanding of reasoning practices and how these are shaped by discursive moves is required in biology education, in order to help students view biological processes in a wider context, and thus gain a better understanding of evolutionary phenomena.

There is emerging interest on the interactions between modelling and argumentation in specific contexts, such as genetics learning. It has been suggested that modelling might help students understand and argue on genetics. We propose modelling gene expression as a way to learn molecular genetics and diseases with a genetic component. The study is framed in Tiberghien’s (2000) two worlds of knowledge, the world of “theories & models” and the world of “objects & events”, adding a third component, the world of representations. We seek to examine how modelling and argumentation interact and connect the three worlds of knowledge while modelling gene expression. It is a case study of 10th graders learning about diseases with a genetic component. The research questions are as follows: (1) What argumentative and modelling operations do students enact in the process of modelling gene expression? Specifically, which operations allow connecting the three worlds of knowledge? (2) What are the interactions between modelling and argumentation in modelling gene expression? To what extent do these interactions help students connect the three worlds of knowledge and modelling gene expression? The argumentative operation of using evidence helps students to relate the three worlds of knowledge, enacted in all the connections. It seems to be a relationship among the number of interactions between modelling and argumentation, the connections between world of knowledge and students’ capacity to develop a more sophisticated representation. Despite this is a case study, this approach of analysis reveals potentialities for a deeper understanding of learning genetics though scientific practices.