Name the gene commonly linked to pelvic girdle reduction in freshwater sticklebacks and describe the resulting phenotype.

Name the gene commonly linked to pelvic girdle reduction in freshwater sticklebacks and describe the resulting phenotype.

• A. Pitx1; loss or reduction of the pelvic girdle/spines
• B. Eda; increase in armor plating
• C. Gad1; pelvic girdle expansion
• D. Pax6; eye reduction

Answer: (A)

Regulatory changes in a developmental gene can drive repeated morphological changes, as seen with pelvic reduction in freshwater sticklebacks. The gene Pitx1 encodes a transcription factor that promotes pelvic development. In freshwater populations, deletions in the pelvic enhancer of Pitx1 reduce its expression specifically in the developing pelvis, so the pelvic girdle and the pelvic spines form poorly or not at all. The resulting phenotype is a loss or major reduction of the pelvic girdle and its spines compared with marine sticklebacks that retain a full pelvis. This pattern illustrates how cis-regulatory changes can lead to parallel evolutionary changes with relatively targeted effects. The other options involve traits not linked to the pelvic girdle: Eda affects armor plating, Pax6 controls eye development, and Gad1 is a neurotransmitter-related gene.

Regulatory changes in a developmental gene can drive repeated morphological changes, as seen with pelvic reduction in freshwater sticklebacks. The gene Pitx1 encodes a transcription factor that promotes pelvic development. In freshwater populations, deletions in the pelvic enhancer of Pitx1 reduce its expression specifically in the developing pelvis, so the pelvic girdle and the pelvic spines form poorly or not at all. The resulting phenotype is a loss or major reduction of the pelvic girdle and its spines compared with marine sticklebacks that retain a full pelvis. This pattern illustrates how cis-regulatory changes can lead to parallel evolutionary changes with relatively targeted effects. The other options involve traits not linked to the pelvic girdle: Eda affects armor plating, Pax6 controls eye development, and Gad1 is a neurotransmitter-related gene.