Provided are methods for amplifying a gene or RNA or sets thereof of interest using a tandem PCR process. The primers in the first PCR or set of PCR reactions are locus-specific. The primers in the second PCR or set of PCR reactions are specific for a sub-sequence of the locus-specific primers and completely consumed during the second PCR amplification. For RNA amplification, the first PCR is reverse transcription and the resulting cDNA(s) provide a template for cRNA synthesis, endpoint PCR or real time PCR. Also provided is a tandem PCR method which accepts raw, completely unpurified mouthwash, cheek swabs and ORAGENE™-stabilized saliva as the sample input, the resulting amplicons serving as the substrate for complex, microarray-based genetic testing. Also provided is a method of allelotyping a gene or set thereof by amplifying the gene(s) using tandem PCR on DNA or RNA comprising the sample.