Since seedless grapes cannot reproduce in the same manner that grapes usually do (for example, dropping seeds), growers have to take cuttings from the plants, root them, then plant the cuttings. Seedless grapes come from a naturally occurring mutation in which the hard seed casing fails to develop. Although the exact origin of seedless grapes is unknown, they might have been first cultivated thousands of years ago in present-day Iran or Afghanistan. Currently, 90 percent of all raisins are made from Thompson seedless grapes.