This paper aims to investigate the conceptions about the relation between genotype and phenotype of Biological Sciences Degree students who take part in a research group in Epistemology of Biology. In an initial data collection, the presence of ideas based on a restricted to genes and environment relation - without considering the organism and its life history - became evident . However, during the group discussions on the topic there were other statements involving other concepts, such as: molecular interactions, chance, organism and Developmental Biology. The analysis of conceptual (re)constructions that emerged in the group allowed the proposition and the development of an explanatory model for the relation between genotype and phenotype.