Theophilus Shickel Painter (August 22, 1889 – October 5, 1969) was an American zoologist known for his work in identifying genes in fruit flies (Drosophila). He did so by applying the incredible detail that had just been discovered to be visible in the giant polytene chromosomes in the salivary glands of Drosophila and other Dipteranlarvae.
Painter joined the faculty at the University of Texas in 1916 and, except for military duty during World War I, stayed there his whole career. He was, in succession, associate professor, professor and distinguished professor of zoology. He served as acting president (1944–1946) and president (1946–1952) of the University of Texas and retired from active teaching in 1966.
Painter was president of the University of Texas when Texas resident Hermon Marion Sweatt applied for and was denied admission due to his race. Subsequently, Painter was the named defendant in the civil rights case Sweatt v. Painter, 339 U.S.629 (1950), which proved an integral stepping stone in the landmark case Brown v. Board of Education of Topeka, Kansas that held that "separate is inherently unequal" and led to the integration of America's public schools.
Painter is also known for his early study of human chromosomes. In 1921 he first gave the number 24 for the count of human meioticchromosomes. He had tried to count the tangled mass of chromosomes he could see under a microscope in spermatocytes in slices of testicle and arrived at the figure of 24. Others later repeated his experiment in other ways and agreed upon the number of 24. Popular thinking held that if there were 24 chromosomes in spermatocytes, there must be an equal number contributed by the female and the human chromosome number must be 48, which was undisputed for more than 30 years.
Then in 1955, Joe Hin Tjio, using more advanced techniques, looked at the chromosomes in human somatic cells and found 46 chromosomes. Together with Albert Levan, Tjio published his finding in early 1956, and the human chromosome number was finally revised.