How are seedless grapes grown?

The correct answer is that the plants that grow them are actually clones. So instead of growing them from seeds, they're grown from cuttings from existing plants. So, obviously, the first seedless grapes were a plant that arose through mutation, that means that they don't have seeds, which some growers must have noticed and propagated. To do this you take a little shoot or a stem off the plant, dip it in rooting powder, put it in the ground and a new tree will grow. This is how a lot of plants are cultivated now, and also a lot of seedless varieties. That said, it's causing problems with bananas now: because they're all clones, they're getting struck down by fungi. If a population is genetically identical, it can very easily be wiped out because all the plants have the same genetic vulnerabilities. If a pathogen evolves to exploit this molecular loophole it's curtains for the crop because every plant is susceptible and the absence of sex means a lack of genetic variation.