system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why scientists have not been able to develop seedless mangoes and avocados?

We have seedless banana's, oranges, grapes and other endless number of fruits that once used to have seeds. If scientists were able to get rid of seeds in them, what are the challenges being faced by them to get these fruits to become completely seedless?
gpt
Most seedless varieties of normally seeded fruits are mutations that don't produce seeds and get propagated by grafting.  It could be such a mutation hasn't been seen in those fruits, or that it's not viable when it happens.