Pel is the pelvic enhancer of which gene?

• A. EDA
• B. Gdf6
• C. Shh
• D. Pitx1

Answer: (D)

Regulatory DNA controls where a gene is active during development, and changes in enhancers can shift a trait. Pel is a pelvic-specific enhancer that drives Pitx1 expression in the developing pelvic region. Because Pitx1 is crucial for pelvic formation, Pel ensures Pitx1 is turned on where the pelvis develops. When Pel is disrupted or deleted in some sticklebacks, Pitx1 isn’t expressed in the pelvis, leading to reduced or absent pelvic structures while the Pitx1 gene itself remains unchanged. This shows how evolutionary changes in regulatory elements can reshape morphology without altering the protein. Pel is not an enhancer for the other listed genes, which have different roles in development.