Genetic identity often differs from the established forms of cultural identity (ethnicity, gender, class, citizenship) or family law status. Over the past two decades, however, we can observe that genetic features have become more and more important elements of personal identity. Genetic testing and genetic screening, paternity testing and forensic identification have emerged as powerful determinants of who we are and whom we can identify with. Advances in genetics have undoubtedly provided useful methods for criminal justice, but they also created new challenges for interpreting forensic research findings in a non-discriminatory way. This paper explores and discusses the current legal dilemmas of using genetic identity in place of personhood in ancestry search, reproduction policy, and in other domains of legal policies, and argues that law should keep the distinction between genetic identity and personal identity in order to avoid the trap of a mereological fallacy.