For each chromosome contributed by the sperm there is a corresponding chromosome contributed by the egg, there are two chromosomes of each kind, which together constitute a pair.

In 1915 Morgan Sturtevant Calvin Bridges and H. George Beadle returned to Caltech to replace Morgan as chairman of the department in 1946. E.

These discoveries formed the basis of the modern science of genetics. In his famous Fly Room at Columbia University Morgan demonstrated that genes are carried on chromosomes and are the mechanical bases of heredity. Following the rediscovery of Mendelian inheritance in 1900 Morgan's research moved to the study of mutation in the fruit fly Drosophila melanogaster.