Which phenotype is associated with Pitx1 variation in freshwater sticklebacks?

Which phenotype is associated with Pitx1 variation in freshwater sticklebacks?

• A. Increased armor plating
• B. Loss or reduction of the pelvic girdle/spines
• C. No pelvic changes
• D. Longer dorsal fin

Answer: (B)

The main idea is how a regulatory change in a developmental gene can reshape a specific part of the body. In freshwater sticklebacks, changes to the pelvic enhancer of Pitx1 reduce or eliminate Pitx1 expression in the developing pelvic region. This targeted decrease leads to loss or reduction of the pelvic girdle and its spines, a common freshwater adaptation that helps these fish in different environments. The gene behind armor plating is typically Eda, not Pitx1, and other pelvic or dorsal features aren’t tied to Pitx1 variation in this context. So the phenotype associated with Pitx1 variation in freshwater sticklebacks is loss or reduction of the pelvic girdle and pelvic spines.

The main idea is how a regulatory change in a developmental gene can reshape a specific part of the body. In freshwater sticklebacks, changes to the pelvic enhancer of Pitx1 reduce or eliminate Pitx1 expression in the developing pelvic region. This targeted decrease leads to loss or reduction of the pelvic girdle and its spines, a common freshwater adaptation that helps these fish in different environments. The gene behind armor plating is typically Eda, not Pitx1, and other pelvic or dorsal features aren’t tied to Pitx1 variation in this context. So the phenotype associated with Pitx1 variation in freshwater sticklebacks is loss or reduction of the pelvic girdle and pelvic spines.