One aspect of the present invention relates to an 
oligonucleotide agent comprising at least one universal 
nucleobase. In certain embodiments, the universal 
nucleobase is difluorotolyl, nitroindolyl, nitropyrrolyl, or nitroimidazolyl. In a preferred embodiment, the universal 
nucleobase is difluorotolyl. In certain embodiments, the 
oligonucleotide is double-stranded. In certain embodiments, the 
oligonucleotide is single-stranded. Another aspect of the present invention relates to a method of altering the expression level of a target in the presence of target sequence polymorphism. In a preferred embodiment, the oligonucleotide agent alters the expression of different alleles of a 
gene. In another preferred embodiment, the oligonucleotide agent alters the expression level of two or more genes. In another embodiment, the oligonucleotide agent alters the expression level of a 
viral gene from different strains of the 
virus. In another embodiment, the oligonucleotide agent alters the expression level of genes from different species.