Chromosome Photography and the Human Karyotype

In 1956, Joe Hin Tjio and Albert Levan published a paper in which they suggested that the number of human chromosomes was 46 and not 48. The story of the recount has been the subject of numerous studies and debates. In this essay I propose to revisit the 1956 paper and the questions surrounding it by considering the chromosome images it contained. Paying attention to the images, including especially the photomicrograph that has come to represent the new chromosome count, offers the opportunity to study the history of an iconic image of genetics. In the course of this history the image moved from proving the quality of Tjio and Levan’s preparations to becoming an object of contention, proof of authorship, example to emulate, manipulable object, recognizable icon, and historical object in its own right. More generally, the essay highlights the role of visual techniques and materials in shaping knowledge and staking claims in human heredity in the mid-twentieth century. The history of postwar cytogenetics has long been overshadowed by dominant accounts of molecular approaches in biology that developed rapidly at the same time. Yet the recognition that, well into the 1970s, chromosome pictures were the most recognizable images of genetics points to the need for new approaches to the historiography.