What does genomic architecture of adaptation refer to in sticklebacks?

• A. The arrangement and effect sizes of genetic loci controlling adaptive traits, often with a few large-effect QTL and many small-effect loci.
• B. The idea that a single gene controls all adaptive traits.
• C. Adaptation is determined solely by environmental factors.
• D. Genomic architecture means all loci have identical effects.

Answer: (C)

Genomic architecture of adaptation describes how genetic variation is arranged across the genome to produce adaptive traits. In sticklebacks, this pattern often involves a mix: a few regions have large effects on key traits, while many other regions contribute smaller effects that fine-tune those traits. For example, a major locus like Eda has a strong impact on armor plate number, showing a large-effect QTL, but numerous other loci scattered across the genome contribute additional, smaller influences on plate morphology, body shape, and other adaptive features. This combination of big-effect and small-effect loci explains how sticklebacks can rapidly adapt to different environments, using both major genetic switches and many supporting tweaks. It’s not about a single gene controlling everything, nor about environment alone, nor about all loci having the same impact.