This paper presents an ethnographic case study of the use of race in two interconnected laboratories of medical genetics. Specifically, it examines how researchers committed to reducing health disparities in Latinos with asthma advance hypotheses and structure research to show that relative frequencies of genetic markers characterize commonly understood groupings of race. They do this first by unapologetically advancing the idea that peoples whom they take to be of the `Old World', or `Africans', `Europeans', `East Asians', and `Native Americans', can serve as putatively pure reference populations against which genetic risk for common diseases such as asthma can be calculated for those in the `New World'. Technologically, they deploy a tool called ancestry informative markers (AIMs), which are a collection of genetic sequence variants said to differ in present-day West Africans, East Asians, Europeans, and (ideally Pre-Columbian) Native Americans. I argue that this technology, compelling as it may be to a range of actors who span the political spectrum, is, at base, designed to bring about a correspondence of familiar ideas of race and supposed socially neutral DNA. This correspondence happens, in part, as the scientists in question often bracket the environment while privileging racialized genetic variance as the primary source of health disparities for common disease, in this case between Mexicans and Puerto Ricans with asthma. With their various collaborators, these scientists represent a growing movement within medical genetics to re-consider race and `racial admixture' as biogenetically valid points of departure. Furthermore, many actors at the center of this ethnography focus on race as a function of their personal identity politics as scientists of color. This to say, they are driven not by racist notions of human difference, but by a commitment to reduce health disparities and to include `their' communities in what they describe as the `genetic revolution'.