What evidence links lateral plate reduction to changes in the EDA regulatory region?

• A. Genomic deletions or functional changes in the EDA regulatory region correlate with plate number reduction across freshwater populations.
• B. Mutation in the EDA coding region disrupting function
• C. Overexpression of EDA gene
• D. Spine changes drive the plate reduction

Answer: (A)

The key idea is that changes in when and where a gene is turned on can drive visible evolutionary differences, without altering the protein itself. In sticklebacks, freshwater populations tend to have fewer lateral plates, and this pattern aligns with alterations in the regulatory region of the EDA gene. Deletions or other functional changes in this regulatory region can lessen EDA expression during the development of dermal plates, leading to fewer plates. Because this regulatory shift is observed across multiple independent freshwater populations, it strongly links changes in EDA regulation to the plate-reduction phenotype.

Coding-region mutations in EDA would affect the protein's function more broadly and wouldn’t necessarily track with plate numbers across different populations. Overexpression of EDA would be expected to increase, not reduce, plate formation. And changes in spine development are a different trait, not the lateral plates themselves.