The first example of association between a marker locus and a quantitative trait was documented in 1923 in a bean species (Phaseolus vulgaris) involving seed size and color. Consider the two parental lines below. Yellow pigmentation is dominant to white.
|Parental line||Color||Seed weight, mg|
|Yellow eye 1317||Yellow||480|
These two lines were crossed to produce F1 individuals, which in turn were interbred to make the F2 generation. The table below shows the genotypes and average seed weights among F2 individuals.
|Genotype||PP (yellow)||Pp (yellow)||pp (white)|
|Average seed weight||307||283||264|
The genotypes of the yellow F2 plants were based on observations of color in their F3 progeny.