Why did Kingsley and his team cross marine and freshwater st

Why did Kingsley and his team cross marine and freshwater sticklebacks?

Solution

The freshwater sticklebacks and the marine sticklebacks differ from each other in the amount of protective armor that cover their bodies. The marine sticklebacks have about 30 plates that extend from head to tail while the freshwater breed has a handful of such plates closer to the front body. When a marine stickleback moves from ocean to freshwater, the low armored survived and reproduce in comparison to the fully armored ones. The Kingsley and his team crossed the both breeds to find out the genes that are responsible for such differences in the marine and freshwater stickleback. By the cross, they were able to study the resulting hybrid offspring and the genes which were making the specific changes.