This investigation was modified from the HHMI Stickleback Modeling activity where students examine two different forms of the the stickleback fish. One form has spines and bony armor and is found in the ocean. The other has less armor and is missing its pelvic girdle, and is found in fresh water lakes.

The activity has students watch the HHMI video showing how the change in morphology was likely an adaptation to sticklebacks becoming isolated in lakes where predators were smaller and spines did not protect them.

Students explore the mystery of how gene regulation changed the expression of the Pitx1 gene which controls the expression of the pelvic girdle, the pituitary and the jaw. The gene itself isn’t altered in freshwater fish, rather the genetic switch has turned off the expression of that gene in the pelvis.

Students label a diagram showing where the regulator switches are relative to the Pitx1 gene. The HHMI modeling activity has an exercise where students use pipe cleaners to model how RNA polymerase attaches to the DNA and facilitates the expression of Pitx1 in the different regions of the fish.