Most seedless grapes are stenospermocarpic, which means the seeds start to
develop after normal pollination and fertilization but abort before maturity.
The remains of the aborted seed(s), called seed traces, can be seen in the
"seedless" fruit.
Grape breeders now use tissue culture to prevent the tiny embryos from
aborting. This technique is called embryo rescue. It allows two seedless grapes
to be crossed and produce viable offspring. Embryo rescue had been a major
reason why there are so many new seedless grape cultivars.

Will it work with bananas? Somebody told me all the banana plants in the world
are dying of an incurable disease. And of course the commercial bananas are
seedless.

Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)