A separation technique; a technique to speed up the task of selecting, from thousands of laboratory specimens, the few cells with precisely the desired genetic changes induced (via genetic engineering). The thousands of genetically altered cells are brought about (produced) by genetic engineering experiments. Many genetic alterations are accomplished by injecting or flooding (specimen) cells with fragments of new genetic material (genes). A few cells are produced that have precisely the desired genetic changes among a large number of cells that do not have the desired changes. Sort of like a “needle in a haystack.” By analogy, the few cells possessing the desired trait represent the needles while the multitude of cells not possessing the trait represent the hay. In order to isolate the few desired cells the needles must be separated from the hay. PNS gets rid of the nondesired cells and leaves only the cells possessing the desired genetic change. This is accomplished in the following way. The pieces of newly injected genetic material are composed not only of the desired sequence of DNA, but also another piece of DNA (known as a marker) which renders only those cells possessing the desired (genetic) change resistant to certain antibiotic drugs (such as neomycin) and certain antiviral drugs (e.g., gancyclovir). When all of the engineered cells are exposed to the drug (which normally kills all of the cells) only those cells possessing the desired genetic change (and the concomitant piece of DNA providing drug resistance) survive and hence are “selected.” The other cells not having the drug resistance are selected against, and die.