Bananas have an odd number of chromosome sets and cannot successfully perform meiosis--the third set has nothing to synapse with. This leads to a lack of gametes and, thus, infertility.
Work Step by Step
Review the material in this chapter and the several immediately before it on issues like crossing over to see the problem presented by the extra/third set of chromosomes in a triploid organism. Being an odd number, there is no way for chromosomes to divide evenly and rejoin to the correct number of chromosomes.