Answer
b
Work Step by Step
In studies conducted on the fruit fly $Drosophila$ $melanogaster$, Alfred Sturtevant found that the farther away two genes were on a chromosome, the more likely they were to cross over; conversely, if two genes are located close to one another, the possibility of them crossing over was small. Using this hypothesis, Sturtevant devised a way of mapping where genes are located on a chromosome based on how often certain genes were found to cross over; his method has been used to make gene maps of other organisms.
