Parallel spindles occur during microsporogenesis in the cultivar Sebago (2n=4x =48) and are the basis of 2n pollen production in this clone. The relations between the frequencies of parallel spindles, 2n microspores, and 2n pollen are striking. The predicted frequency of 2n pollen based on the percentage of microsporocytes with parallel spindles is highly correlated with the frequency of 2n pollen observed. The percentage of 2n microspores at the sporad stage also corresponds very closely with the observed percentage of 2n pollen. Sebago is thus nulliplex (psp sp sps) for the meiotic mutant which governs spindle orientation at the second meiotic division in microsporocytes. This finding agrees with the prediction that if parallel spindles were involved in the origin of cultivated tetraploid potatoes, the genesps should be present in some 4x cultivars. It adds further support to the concept that 2n gametes have been a creative factor in the origin and evolution of cultivated tetraploids.