Crossing between isolate carrying allelic combination of a nonsense mutation and a tRNA nonsense suppressor with isolate without this combination. After meiosis, 25% of the offspring inheriting only the nonsense mutation but not the suppressor were non-viable on conditions with non-fermentable carbon sources, as the nonsense mutation was essential for respiration. Nevertheless, when the nonsense suppressor was introduced other genetic background, it could confer to gain or loss of fitness in different environmental conditions, possibly indicating an adaptive role of certain incompatible alleles in complex ecological contexts.