Which statement best describes a quantitative trait locus (QTL)?

Which statement best describes a quantitative trait locus (QTL)?

• A. any part of the genome that affects traits of interest
• B. a region of the genome that affects only one trait
• C. a region of the genome with no impact on phenotype
• D. a non-genetic factor

Answer: (A)

A QTL is a region of the genome that contributes to variation in a quantitative trait. It’s not about a single gene alone; a QTL can span multiple genes and may influence one or several traits, with its effect often being small and distributed across the genome. In practice, QTLs are identified by linking genetic markers to differences in phenotype across individuals, showing that this genomic region helps explain part of the trait’s variation. Why the other ideas don’t fit: a QTL is not limited to affecting only one trait—regions can impact multiple correlated traits or show pleiotropy; it is not a region with no impact on phenotype; and it is not a non-genetic factor, since it is defined by genetic variation.

A QTL is a region of the genome that contributes to variation in a quantitative trait. It’s not about a single gene alone; a QTL can span multiple genes and may influence one or several traits, with its effect often being small and distributed across the genome. In practice, QTLs are identified by linking genetic markers to differences in phenotype across individuals, showing that this genomic region helps explain part of the trait’s variation.

Why the other ideas don’t fit: a QTL is not limited to affecting only one trait—regions can impact multiple correlated traits or show pleiotropy; it is not a region with no impact on phenotype; and it is not a non-genetic factor, since it is defined by genetic variation.