What is the role of the EDA regulatory region in plate variation among sticklebacks?

• A. It encodes the EDA protein.
• B. It regulates expression of EDA; mutations here can alter plate number without coding changes.
• C. It controls pelvic spine development.
• D. It has no effect on plate numbers.

Answer: (B)

Gene regulation can drive morphological variation, and in sticklebacks the EDA regulatory region is the switch that matters. This region controls when, where, and how much the EDA gene is expressed during the development of bony plates. Mutations here don’t change the EDA protein itself; they change its expression pattern. That means plate number can shift up or down without altering the protein’s sequence, producing the observed differences between populations that live in freshwater versus marine environments. Regulatory changes allow precise, tissue-specific effects with fewer unintended consequences than altering the protein-coding region.

The other possibilities miss the key point: this region does not encode the EDA protein, it does not regulate pelvic spine development, and it does have a meaningful effect on plate numbers.