The pollination process requires a carrier for the pollen, which can be animal, wind, or human intervention (by hand-pollination or by using a pollen sprayer). Cross pollination produces seeds with a different genetic makeup from the parent plants; such seeds may be created deliberately as part of a selective breeding program for fruit trees with desired attributes. Trees that are cross-pollinated or pollinated via an insect pollinator produce more fruit than trees with flowers that just self-pollinate. In fruit trees, bees are an essential part of the pollination process for the formation of fruit.