Cross the F1's proceed as above. We know that the phenotype and the genotype are not exactly the same thing. So how does this work. Let's think about height- human height. It is an environmental effect.
Plants are the same.
Not only the genetic potential that a plant has but nutrients and weather. This equation forms the basis of much of quantitative genetics. So if the relationship between genotype and phenotype is strong then selecting on the phenotype will produce a string response to selection and the gain from selection will be high. If the relationship is weak or obscured by environmental interactions then selection on the phenotype will be less successful. The amount of heritability observed is the quantification of the relationship between genotype and phenotype.