Seedless watermelon, salmon, and strawberries all have one thing in common - unlike most eukaryotic multicellular organisms that have two sets of chromosomes, these organisms are all polyploid, meaning they have three or more sets of chromosomes. Seedless watermelon and salmon have 3 and 4 sets of chromosomes, respectively, while strawberries have 10.
Most plant species are polyploid. Polyploidy, or genome doubling, was first discovered over a century ago, but only recently, with the development of molecular tools, has it been revealed just how ubiquitous it is. Polyploidy is being increasingly recognized as an important evolutionary force that can facilitate positive adaptations, lead to instant speciation, and increase biodiversity.