In dandelions, the texture of the petals is known to be a quantitative trait; texture can vary between smooth and pockmarked. A cross is made between a smooth parent and a pockmarked parent (the two phenotypic extremes), and then the F1 offspring are crossed to each other. Nine phenotypic categories are identified among the F 2 offspring. How many genes are likely to be directly involved in determining the variation in the texture of dandelion petals?

a) three
b) four
c) six
d) eight
e) nine