What is a QTL in sticklebacks used to identify?

• A. A chromosomal rearrangement with no effect
• B. A phenotype measurement
• C. Regions of the genome associated with variation in traits such as armor plates, spine length, or gill raker number
• D. A single gene causing all variation

Answer: (C)

A QTL is a region of the genome that correlates with variation in a measurable trait across individuals. In sticklebacks, researchers study traits like armor plates, spine length, or gill raker number, which vary between fish and populations. By scanning the genome with genetic markers and measuring these traits in many individuals, they look for statistical associations between marker differences and trait differences. The regions that show a link are QTLs, and each QTL can contain one or more genes or regulatory elements that influence the trait. Often several QTLs contribute to a trait, with varying effect sizes. This is why the best description is that QTLs are regions of the genome associated with variation in traits such as armor plates, spine length, or gill raker number. A chromosomal rearrangement with no effect isn’t what QTL refers to, a phenotype measurement is the trait value, not the genomic region, and a single gene rarely accounts for all variation across a trait.