Based on ethnographic and archival research conducted on North American Judaism and Messianic Judaism, this article argues that each group uses DNA in what appear to be sociologically similar ways but that actually differ profoundly at the theological level. Our analysis moves beyond DNA testing per se to focus on what anthropologist Kim Tallbear calls "gene talk," referring to "the idea that essential truths about identity inhere in sequences of DNA." Contrasting Jews and Messianic Jews, we demonstrate clearly what scholars have only begun to recognize: how theological commitments may drive investments in genetic science and interpretations of it. Further, we show how religiously significant identities associated with race, ethnicity, or lineage interact with DNA science, coming to be viewed as inalienable qualities that reside in the self but move beyond phenotype alone. Finally, we argue that gene talk in these contexts is a religiously inflected practice, which serves to binds communities and (implicitly or explicitly) authorize existing theological ideals.