Fig. 2

Data figures used to calculate heritability in a class of 32 students. Both figures plot average trait value between the two parents (mid-parent trait value) and the trait values for each resulting offspring. The slope of the best-fit line through these points estimates heritability. The regular exercise resulted in a heritability of 1.0 (a). The inclusion of random environmental effects on the phenotype dramatically reduced the heritability (b)