system
Given the following post, respond as if you're commenting on Reddit:
human
How are seedless watermelon grown if they are seedless?
gpt
They are the result of breeding diploid watermelons (two sets of chomosomes) with tetraploid watermelons (4 sets).  The resulting seeds when grown are triploid watermelon plants.

Triploid organisms are almost always sterile, because the odd number of sets of chromosomes can't line up properly during meiosis.  Seedless triploid watermelon plants are exposed to regular pollen, and the plants then make fruit but no seeds.  Seeds are the next generation of watermelons, and in this case, the triploid melons can't make seeds.

Most animals can't handle having more than two sets of chromosomes - almost all are diploid.  Plants can sometimes become tertraploid due to errors in reproduction.  Unlike animals, many plants can handle having 4 or even 6 sets of chromosomes.