In studies of mapping traits like plate number in sticklebacks, what type of data is essential alongside genotype data?

• A. Phenotypic measurements across individuals in cross populations.
• B. Only geographic coordinates.
• C. Only environmental data.
• D. Random sampling without phenotype.

Answer: (A)

To map a trait like plate number to genetic variation, you must have measurements of the trait for each individual in the study in addition to their genotypes. This phenotypic data provides the variation that you can correlate with genetic variants, enabling analyses that link specific genomic regions to differences in the trait. In cross populations, measuring the trait across many individuals creates the signal needed to detect associations or linkages between genotype and phenotype. Geographic coordinates or environmental data can help interpret results or control for population structure, but they aren’t the essential data required to establish genotype–phenotype associations. Random sampling without phenotype yields no information about which genes influence the trait.