Generic diversity for means the division of something like a generic division of a plant or of a group of humans separating them by either ethnicity, age and poverty levels. Generic variation is more a mix of something other than dividing it.
A good example of generic variation is me mixing pennies, nickels and dimes all together in one hand. You are mixing all the coins in one hand and they are all someway or another; different.
Generic diversity in the other hand is separating the pennies, nickels and dimes and classifying by there values and worth. You never mix them together in this case, you keep them separated.