ABSTRACT
X chromosome while females had two. Morgan hypothesized that the recessive character "white eyed" resided on the X chromosome, thus explaining why the white eyed progeny were males. This constituted the first proof that a hereditary character was linked to a chromosome. Characters on the X chromosme were subsequently called sex linked characters. Other work on Drosophila genetics was carried out by Morgan and the remarkably talented researchers (Alfred Sturtevant, Calvin Bridges and Hermann Joseph Muller) who were attracted to Morgan's laboratory. The Belgian cytologist F. Jansens had presented a theory of recombination involving material exchange between homologus chromosomes in meiosis. Subsequently, the Morgan group discovered genetic linkage among mutants on the same chromosome and showed that crossover frequencies could be used to construct a linear genetic map of a chromosome. These results were interpreted as being consistent with the Janssens' in a general theory of linkage elaborated by Morgan. The work of Morgan and his group on chromosomes and their genetic structure provided the basis for modern genetic analysis and, in addition, provided a chromosomal equi-valent for the gemmules in Darwin's theory of pangenesis. After the years at Colombia University, the last part of Morgan's career was spent at the California Institute of Technology in Pasadena. It was there that he created the research group that Georges Beadle joined in 1931 as a post doctoral fellow. Morgan and his group established an ideal environment in which Max Delbrück and George Beadle (who had returned to Cal
Tech as Chairman of the Division of Molecular Biology) were to make significant contributions to the beginnings of molecular biology.
