Joseph Grafton Gall researched and taught cell biology for over seventy years in the late twentieth and early twenty-first centuries in the United States. Much of his early work revolved around the structure and function of chromosomes, which are structures made of DNA and protein found in cells. As a professor at Yale University in New Haven, Connecticut, Gall and his graduate student Mary-Lou Pardue developed in situ hybridization, a technique that uses probes to identify the location of specific DNA sequences along a chromosome. With another graduate student, Elizabeth Blackburn, he also performed research on the structure of telomeres, which are the ends of chromosomes. Gall was an early advocate for women in STEM and trained many female scientists, many of whom became successful in their fields. Gall studied the structure and function of different forms of genetic information, namely DNA and RNA, helping to expand the understanding of how those molecules replicate within cells.