The correct option is B Thomas Hunt Morgan
The findings of Mendel brought light to the field of genetics and provided the foundation for the modern theory of genetics. Many more discoveries happened in the field of genetics in the early 1900s. Two scientists namely - Walter Sutton and Theodor Boveri, working independently, unified the knowledge of chromosomal segregation with the Mendelian principles and proposed the chromosomal theory of inheritance. However, the precise experimental verification of the theory was given by an American scientist, Thomas Hunt Morgan in 1910, by performing breeding experiments on Drosophila melanogaster.
Alfred Sturtevant is one of the students of Morgan, who performed most of the experimental research on Drosophila to study heredity and constructed the first genetic map of a chromosome.