The Scatterplots Below Show the Relation Between the Average Phenotype

Multiple Choice

The scatterplots below show the relation between the average phenotype of parents (x-axis) and that of their offspring (y-axis) for three traits. One trait has a heritability of 90% (comparable to that of fingerprint ridge count) , another has a heritability of 50% (comparable to that of human height) , and yet another has a heritability of 25% (comparable to that of human longevity) . To make the axes comparable, for each trait the phenotypic measurement is expressed as a deviation from the overall mean in multiples of the standard deviation.
The fact that all of the lines slope upward means that:

A) variation in each trait is affected by differences in heredity.
B) variation in each trait is affected by environmental differences.
C) the genes affecting any one trait have no effect on any other trait.
D) some genes affect all three traits.
E) the traits all show genotype-by-environment interaction.