"Biological identity" is the result of interactions between the environment and the genome. These interactions, however, were not taught before 2001. In the French syllabus for 16-year-old students, two of the five sections on genetics deal with biological identity. We analysed the texts and images of the chapters relating to these two sections in the three most commonly used textbooks. The results showed that, using strategies specific to each textbook, all focused predominantly on the genetic determination of the phenotype, and on the idea of the "genetic code". We then analysed the conceptions of 35 trainee Biology teachers, using their answers to a questionnaire. For most of them, psychological identity does not illustrate the notion of biological identity: the Cartesian dualism of body/soul is very influential. The analysis of the trainee teachers' conceptions showed their poor understanding of genome/environment interactions and of the process of epigenesis. Fortunately, since 2001, in France genome/environment interactions have been introduced into the new Biology syllabus. (Contains 13 figures.)