The Pitx1 gene has been identified as involved in which two major traits?

• A. Pitx1 is involved in pelvic spines in stickleback fish, and hind limb development in other vertebrates.
• B. Pitx1 has no role in pelvic spine formation.
• C. Pitx1 is only involved in hind limb development.
• D. Pitx1 is involved in brain development.

Answer: (D)

Pitx1 is a gene that helps shape the development of limbs and other appendages. In many vertebrates it plays a key role in hind limb formation. In stickleback fish, changes in the regulatory region that controls Pitx1 expression specifically in the pelvic region lead to the loss or reduction of pelvic spines. This shows how the same gene can influence different morphological traits across species through changes in when and where it is turned on. Brain development is not the typical trait linked to Pitx1 in this context. The two major traits associated with Pitx1 are pelvic spines in sticklebacks and hind limb development in other vertebrates.