Which genes are commonly cited as large-effect QTL for armor plate number in sticklebacks?

• A. Pitx1 and BRCA1.
• B. Eda and FOXP2.
• C. Pitx1 and MC1R.
• D. Eda and Pitx1.

Answer: (D)

Armor plate number in sticklebacks is a trait that evolves largely through a few genes with big effects. The standout player is Eda, where regulatory changes reduce armor plating in freshwater populations by altering the ectodysplasin signaling pathway. A second major contributor identified in multiple studies is Pitx1, a developmental gene that affects skeletal structures and can explain substantial variation in plating in some populations. Together, these two loci account for a large portion of the differences seen between marine and freshwater sticklebacks, illustrating how a small number of powerful genetic changes can drive major adaptive changes. The other genes listed are linked to very different traits (DNA repair, language-related function, and pigmentation) and aren’t the well-established major-effect QTL for armor plates.