Sizing Dna Fragments by Ultrasensitive Flow Cytometry

As originally developed in the 1960's, flow cytometry was primarily a technique for the analysis of mammalian cells. Analysis of cellular constituents such as DNA or cell surface antigens made fluorescent by a variety of reagents has been the main stay of flow cytometric applications. Over the years, flow cytometric analysis techniques have been developed that range from multicellular spheroids containing a million or more cells down to single molecule detection. An outgrowth of single molecule detection capability is DNA fragment size analysis. DNA fragment size analysis starts with a sample of naked DNA that can be derived from a variety of sources including PCR products, double stranded viral genomes, BAC/PAC clones, and bacterial genomes. For genomic or cloned DNA, restriction enzyme digests are analyzed to produce a fingerprint pattern. The fingerprint, i. e., the distribution of fragment sizes produced by the restriction enzyme digestion, is characteristic of the source of DNA and forms the basis for identifying the source.