This dissertation examines the visual cultures of postwar biomedicine, with a particular focus on how various techniques, conventions, and professional norms have shaped the look', classification, diagnosis, and understanding of genetic diseases. Many scholars have previously highlighted the informational' approaches of postwar genetics, which treat the human genome as an expansive data set comprised of three billion DNA nucleotides. Since the 1950s however, clinicians and genetics researchers have largely interacted with the human genome at the microscopically visible level of chromosomes. Mindful of this, my dissertation examines the `observational' approaches of postwar genetics. This is accomplished through a series of case studies, which examine the visual delineation, diagnosis, and genomic localization of a number of disorders. My case studies explore various exemplary attempts to associate particular clinical disorders with specific genetic mutations. This dissertation uses archival resources, oral histories, and the published biomedical literature to examine the many successes of postwar biomedicine, and to highlight the contributions made by a wide rage of biomedical professionals. I find that the visible, tangible human genome, as conceived and depicted at the level of chromosomes, has become an important work object among a diverse array of practitioners. Chromosomal ideograms, I argue, provide an important basis for communication and common practices among this community. While genetic data is becoming increasingly significant to our understanding of human disease, distinguishing the normal from the pathological remains a task that relies on input from the laboratory and the clinic. Thus, the success of postwar genetic medicine must be seen in light of the contributions of biomedical actors from many disciplines, who have agreed to see and communicate about the human genome - their object of study - in standardized ways.