Frequency of unreduced pollen grains was estimated for five genotypes of Solanum phureja (2n=24) growing in three environments; (E1) cool (7.2-13.3°C) and (E2) warm (12.2-17.2°C) growth chambers and (E3) field conditions. Highly variable frequencies were found, with genotype, environment, and genotype x environment interaction as significant components of variance. The frequency of unreduced gametes for two additional genotypes was studied over time in two growth chamber environments (cool and warm). One genotype, characterized by mostly fused spindles at the second meiotic division, expressed a high frequency of big pollen (BP) in both environments, whereas the second, characterized by fused, parallel and tripolar second division spindless was found to increase in BP frequency over time in the cool chamber, but remained consistently low in the warm chamber. The identification of specific environmental components with general effect on the expression of un-reduced gametes is not possible because of the large genotype x environment interaction component of variance. A genetic hypothesis based on incomplete penetrance and variable expressivity of a dominant gene is presented as an alternative to the currently accepted theory of control of parallel spindles by a single recessive gene.