State the contribution of the following scientists: Thomas Hunt Morgan and Alfred Sturtevant.

What map unit (Centimorgan) is adopted in the construction of genetic maps?

Define/Explain: Linkage.

Which scientist explained linkage and recombination in Drosophila?

The term 'crossing over' was coined by

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