 Most instances of autopolyploidy result from the fusion of unreduced (2"n") gametes, which results in either triploid ("n" + 2"n" = 3"n") or tetraploid (2"n" + 2"n" = 4"n") offspring.Triploid offspring are typically sterile (as in the phenomenon of 'triploid block'), but in some cases they may produce high proportions of unreduced gametes and thus aid the formation of tetraploids.This pathway to tetraploidy is referred to as the “triploid bridge”.