Morgan, Sturtevant, Muller & Bridges Show that Mendelian Laws are Demonstrated by Observable Events Occurring in Cells

In 1915 American zoologist and geneticist Thomas Hunt Morgan, and his students and co-workers in the Fly Room at Columbia University: Alfred H. Sturtevant, Hermann J. Muller and Calvin B. Bridges published The Mechanism of Mendelian Heredity. Summarizing the research the team had done since 1910, this widely read textbook presented evidence that genes are arranged linearly on chromosomes, and that Mendelian laws are demonstrated by observable events occurring in cells.

"By 1915 Morgan and his co-workers were able to present the locations on a genetic map for 30 distinct genes of the four Drosophila chromosomes" (Brock pp. 14-15)