Disclosed are methods for detecting DNA mutations of target genes in a DNA sample by combining single-molecule clonal amplification and mutant primer specific extension detection. In the method, thousands and millions of DNA molecules are locally amplified to form immobilized DNA clusters of identical sequences. Mutation specific primers are used to anneal to the mutant sequences in the DNA clusters and are extended by DNA polymerase to make labeled DNA strands. The labeled DNA clusters are detected to identify the DNA clusters of mutant sequences. This method enables detection of single mutation molecule and direct enumeration of mutation molecules in the sample. Once generated from a DNA sample, the immobilized DNA clusters can be reused many times for detection of different mutations or sequences of interest. Methods for determining differential gene expression and chromosome copy number variation are also disclosed.