Abstract: A method for quantitatively determining the relative copy number of a gene of interest introduced recombinantly into a cell is disclosed. The method includes the steps of propagating, in a suitable culture medium, cells that are transformed with a chimeric gene construct containing and capable of expressing the gene introduced into the cells, where said construct includes (i) a control nucleic acid segment having a region of DNA capable of hybridizing with a region of native genomic DNA associated with the cell; and (ii) a second nucleic acid region that contains said gene of interest; isolating DNA from the cells; and determining the ratio of the control nucleic acid segment to the region of native genomic DNA in the isolated DNA as a quantitative measure of the relative copy number of the gene in the cell.