In this paper, I explore the origins of medical cytogenetic knowledge and practices in the 1960s and 1970s in Mexico, focusing on the work of the group headed by Salvador Armendares, who spent two years in Oxford, England, with human genetics expert Alan C. Stevenson. Upon Armendares’ return from England in 1966, the first Unit for Research in Human Genetics was created at a medical setting, the Instituto Mexicano del Seguro Social (Mexican Institute of Social Security). Soon after its creation, Fabio Salamanca and Leonor Buentello began to work with Armendares in the implementation of cytogenetics. Some of the research projects showed the embeddedness of these researchers in both public health policy and medical care, as they tackled the effects of malnutrition on chromosome structure, child mortality, chromosome aberrations, and Down syndrome. Armendares, Salamanca, and Buentello had trained at different academic institutions at many different times, and contributed to transforming hospital medical practice into a medical research discipline. By posing malnutrition, one of the main concerns of Mexican post-revolutionary governments, as both a medical and a genetic problem, the unit contributed to positioning cytogenetics as a medical practice and a medical research domain. The focus of this paper will be this set of institutions, physicians, practices, and ideas that began to reshape medical genetics in Mexico. The reconstruction of the early days of cytogenetics in Mexico demonstrates the major roles played by both the clinic and post-revolution public health policies in the origins of medical genetics in Mexico, within a global movement to deliver the benefits of scientific knowledge to the general population.