Which statement best summarizes Pitx1's role as described in the material?

• A. Pitx1 is involved in pelvic spines formation in sticklebacks and hind limb development in other vertebrates.
• B. Pitx1 is involved in pelvic spines formation in sticklebacks.
• C. Pitx1 is involved in hind limb development in other vertebrates.
• D. Pitx1 is involved in brain development.

Answer: (D)

Pitx1 has roles in different developmental contexts across species: in sticklebacks it influences pelvic spine formation, while in other vertebrates it’s involved in hind limb development. The best summary is the one that mentions both of these contexts because it reflects the material’s description of Pitx1 functioning in pelvic structures in sticklebacks and in hind limbs elsewhere. The other options miss part of this picture—one only notes pelvic spines, another only hind limbs, and none mention brain development as a role for Pitx1 in this material.