Walter Sutton first related genetics to the behavior of chromosomes in 1902, showing that the grasshopper Brachystola has 11 pairs of homologous chromosomes, and that each sex cell formed during meiosis receives one of each pair as a consequense of meiosis. By demonstrating that these are independently assorted during meiosis, following Mendel's observations for hereditary factors, he was able to suggest that genes were located on chromosomes.
 

Edmund Wilson, Sutton's mentor at Columbia University, and Nettie Stevens demonstrated the first direct link between chromosomes and heredity by showing that sex determination is governed by separate X and Y chromosomes.