Figure 24.17: The narrow-sense heritability, h2, equals the regression coefficient, b, in a regression of the mean phenotype of the offspring against the mean phenotype of the parents. (a) there is no relation between the mean parental phenotype and the mean offspring phenotype. (b) the mean offspring phenotype is the same as the mean parental phenotype. (c) Both genes and environment contribute to the differences in phenotype.