Some have argued that advances in molecular genetics will lead to the geneticisation of identity and the subsequent reduction of the human subject to their genetic complement. In this article, we advance the more cautious argument that far from reducing subjectivity to genetics, genetic knowledge is incorporated and resisted in complex ways. We draw our analysis from a sample of individuals who have attended a clinical genetic service in South Wales. In-depth qualitative interviews (n=61) were conducted with family members to explore the ways in which genetic risk foregrounds patterns of relatedness and responsibility. A surprisingly high incidence of non-disclosure of risk was reported in our study. Families provided complex explanations of guilt, blame, character and surveillance to justify deferring or delaying disclosure of risk. We explain these findings in terms of conditions immanent to the materiality of everyday experience. Our account of ‘practical ethics’ combines discursive and pre-discursive explanations to explore the role of inheritance, kinship and affect in the modulation of genetic responsibility.