Linkage decreases the frequency of

For the preparation of genetic maps, the recombination frequencies between genes are additive over short distances but not over long distances due to

Who clearly proved and define linkage?

In Drosophila, long wing and broad abdomen characters are dominant over to characters vestigeal wing and narrow abdomen. A pure breeding Drosophila having long wings and broad abdomen is crossed with a pure breeding vestigeal-winged and narrow-abdomened Drosophila. Two of the $F_1$ individuals were crossed and the following results were produced in the $F_2$ generation Long wing, broad abdomen in $482$ Drosophila. Vestigeal wing, narrow abdomen in $154$ Drosophila. Which one of the following is illustrated by these results

Discuss in detail the contributions of Morgan and Sturtevant in the area of genetics.