This paper studies the emergence of human population genetics and cytogentics in the post-war Mexico (1945-1970), emphasizing the global circulation of knowledge, people, and scientific practices, and the institutions involved that enabled the consolidation of human genetics in the country. This paper will focus on the work and contributions of Mexican physicians Rubén Lisker and Salvador Armendares. The study of population genetics was the first branch of human genetics that was developed in Mexico. Lisker graduated from the School of Medicine at the UNAM in 1948. He spent four years (1953-57) at the Michael Reese Hospital of Chicago to pursue research on hematology under Karl Singer. While at Chicago, Lisker met Arno Motulsky, who is considered one of the founders of today´s pharmaco-genomics. Since he returned to Mexico in the late 1950s, Lisker´s research laboratory at the Hospital de Enfermedades de la Nutrición focused on the relation between anthropological considerations and medical applications. Following the 1960s trend and technologies he focused on enzymes and other blood components, like the deficiency of the Glucose-6-Phosphate-Dehydrogenase (D6PD) and the presence of abnormal hemoglobins and albumins in Mexican indigenous population. Salvador Armendares graduated from the School of Medicine in 1950 at the UNAM, and specialized in pediatrics at the Children´s Hospital of Mexico in 1956. He spent two years as graduate student at the British Medical Research Council in Oxford (1964-65) under the supervision of Dr. Alan Stevenson, who was at the time the dean of the Council and considered one of the first physicians to work on clinical genetics. The first Unit for Research in Human Genetics in the country was launched in 1966 at the Mexican Institute of Social Security upon Armendares´ return from England. The unit on human genetics contributed to exploring the effect of severe protein calorie malnutrition on chromosome structure, chromosome aberrations, and the effect of mutagenic agents on chromosomes, and in the late 1970s medical problems with new methods of chromosome banding. Armendares was the first to conduct investigations on Down and Turner Syndromes chromosome characterization, some of which were done with Lisker´s collaboration.