Provided are nucleic acids and expression vectors having a non-silencing selectable marker gene, and methods of using the same. A subject expression vector includes an expression cassette and a non-silencing selectable marker gene. In some cases, the non-silencing selectable marker gene provides for drug resistance for prokaryotic cells, and includes a nucleotide sequence that (i) encodes a drug selectable marker protein; (ii) is operably linked to a promoter functional in prokaryotic cells, and (iii) includes an increased A/T content relative to a corresponding wild type nucleotide sequence. In some cases, the non-silencing selectable marker gene provides for drug resistance for prokaryotic cells, and includes a nucleotide sequence that (i) encodes a drug selectable marker protein; (ii) is operably linked to a promoter functional in prokaryotic cells, and (iii) has an A/T content in a range of from 52% to 70%.