The article introduces a method called Digital PCR (Dig-PCR) developed by Bert Vogelstein and Kenneth Kinzler to detect predefined mutations in a small fraction of a cell population. The method transforms the exponential nature of PCR into a linear, digital signal, making it suitable for various applications in basic research and clinical settings. Single molecules are isolated and individually amplified by PCR, and each product is analyzed separately using fluorescent probes to detect the presence of mutations. The feasibility of the approach is demonstrated by detecting a mutant ras oncogene in the stool of patients with colorectal cancer. The process provides a reliable and quantitative measure of the proportion of variant sequences within a DNA sample. The article details the materials and methods used, including the optimization of PCR conditions and the design of molecular beacon (MB) probes. The results show that Dig-PCR can effectively distinguish between wild-type and mutant sequences, with the ratio of RED/GREEN fluorescence indicating the fraction of mutant alleles. The method is also applied to DNA from tumor cells and stool samples, demonstrating its practical utility in detecting rare mutations. The authors discuss the potential applications of Dig-PCR in genetic analysis, including the detection of rare alleles, allelic imbalance, and gene expression quantitation.The article introduces a method called Digital PCR (Dig-PCR) developed by Bert Vogelstein and Kenneth Kinzler to detect predefined mutations in a small fraction of a cell population. The method transforms the exponential nature of PCR into a linear, digital signal, making it suitable for various applications in basic research and clinical settings. Single molecules are isolated and individually amplified by PCR, and each product is analyzed separately using fluorescent probes to detect the presence of mutations. The feasibility of the approach is demonstrated by detecting a mutant ras oncogene in the stool of patients with colorectal cancer. The process provides a reliable and quantitative measure of the proportion of variant sequences within a DNA sample. The article details the materials and methods used, including the optimization of PCR conditions and the design of molecular beacon (MB) probes. The results show that Dig-PCR can effectively distinguish between wild-type and mutant sequences, with the ratio of RED/GREEN fluorescence indicating the fraction of mutant alleles. The method is also applied to DNA from tumor cells and stool samples, demonstrating its practical utility in detecting rare mutations. The authors discuss the potential applications of Dig-PCR in genetic analysis, including the detection of rare alleles, allelic imbalance, and gene expression quantitation.