Originally a marine species, stickleback fish now live in both marine and freshwater environments. marine sticklebacks have pelvic spines that protect them from marine predators. freshwater sticklebacks do not have pelvic spines, which reduces their likelihood of being caught by freshwater predators that can grasp onto these spines. the lack of spines in freshwater sticklebacks results from a heritable mutation that modifies the function of the pitx1gene. this mutation occurred:

a.
in the mrna that is transcribed from the pitx1 gene in pelvic cells.

b.
in the regulatory region of the pitx1 gene.

c.
in the coding region of the pitx1 gene.

d.
in the cells of the pelvis of freshwater sticklebacks.