Ploidy level affects fertility
Autopolyploids with an odd ploidy level (3x, 5x, 7x etc) are usually self sterile. Banana is a good example. It is a triploid (most desert bananas are AAA, most plantains are AAB and the East African cooking types are ABB). All are sterile – otherwise the fruit would be full of seeds!
Diploid BB banana Musa balbisiana