Method of measuring the quantity of a variety of analytes, including DNA, RNA, and protein, by comparison with a known standard; can be used to determine the number of copies of a sequence of DNA (i.e., to test for duplication and deletion mutations) either by visual comparison of band intensity or numerical quantification by densitometry. If extra copies of a gene are present, intensity is greater than 100% on a gel or film; whereas, if one copy of the gene is missing, the intensity is approximately 50%.