How do they continue to grow seedless fruits? How were their seeds first acquired?

Answer 1

Seedless fruits can develop in one of two ways: either the fruit develops without any fertilization (parthenocarpy), or pollination triggers fruit development but the ovules or embryos abort without producing mature seeds (stenospermocarpy). Seedless fruits of banana and watermelon are produced on triploid plants, whose three sets of chromosomes prevent meiosis from taking place and thus do not produce fertile gametes. Such plants can arise by spontaneous mutation or by hybridization between diploid and tetraploid individuals of the same or different species. Some species, such as pineapple and cucumber, produce seedless fruit if not pollinated, but produce seeded fruit if pollination occurs.

Answer 2

There are many ways to propogate/grow plants without using seeds. In fact, some plants best grown from cuttings. Fig trees are an example, but this applies to many other types of fruit trees too.

The main method is you can take cuttings.
Plants are unique in the sense that you can cut off a piece and roots will grow from the cutting. Nature's form of cloning.

Also, some seedless fruit are hybrids/cross-pollinated from seeded fruits.

Answer 3

It's done by grafting, where they splice one vine/branch of a plant onto another and that's how they produce seedless fruits.

Answer 4

it all has to do with the vines, for grapes and such, or the tree, for oranges and such. not so much about the seeds.