A phenotypic ratio for a hybrid cross is predicted to be 9:The experimental values are purple smooth =75 white smooth= 28 purple wrinkled= 24 white…

A phenotypic ratio for a hybrid cross is predicted to be 9:3:3:1. The experimental values are purple smooth =75 white smooth= 28 purple wrinkled= 24 white wrinkled=8. Account for the difference between the expected and experimental values?