Methods of repressing expression of a recombinant gene in a cell are provided. The methods include the steps of introducing a transposase DNA binding motif into or adjacent to the gene, and introducing into the cell a transposase that is capable of binding to the transposase DNA binding motif. Methods of producing a population of cells of an organism that vary in their expression of a gene are also provided. The methods involve transfecting the cells with a first polynucleotide sequence encoding the target gene operably linked to a promoter such that the target gene is expressed in the cells, wherein the vector has at least one transposase DNA binding motif within or adjacent to the target gene; and transfecting some of the cells with a second polynucleotide encoding the transposable element operably linked to a second promoter such that the transposable element is expressed in the cells. In these methods, the target gene in the cells transfected with the second polynucleotide exhibits reduced expression when compared to the target gene in the cells that are not transfected with the second polynucleotide. Kits having a first polynucleotide with a gene and a DNA transposase binding motif in or adjacent to the gene, and a second polynucleotide comprising a gene encoding a transposase that is capable of binding to the transposase DNA binding motif are also provided.