Calvin Bridges Discovers Nondisjunction

In 1913 Calvin Bridges, a genetics student of Thomas Hunt Morgan at Columbia University, discovered nondisjunction (non-disjunction)— the failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2.

Bridges, "Non-Disjunction of the Sex Chromosomes of Drosophila," Journal of Experimental Zoology 15 (1913) 587-606.

Bridges expanded his research into "a masterful Ph.D. thesis"  entitled on "Non-disjunction as Proof of the Chromosome Theory of Heredity," Genetics 1, no. 2 (March 1916) 107-163.