according to the type of gel that is being run—i.e. parallel or perpendicular—the voltage is adjusted and the sample can be left to run. Depending on which type of TGGE is to be run, either perpendicular or parallel, varying amounts of sample need to be prepared and loaded. A larger amount of one sample is used with perpendicular, while a smaller amount of many samples are used with parallel TGGE. Once the gel has been run, the gel must be stained to visualize the results. While there are a number of stains that can be used for this purpose, silver staining has proven to be the most effective tool. The DNA can be eluted from the silver stain for further analysis through PCR amplification. Applications TGGE and DGGE are broadly useful in biomedical and ecological research; selected applications are described below. Mutations in mtDNA According to a recent investigation by Wong, Liang, Kwon, Bai, Alper and Gropman, TGGE can be utilized to examine the mitochondrial DNA of an individual. According to these authors, TGGE was utilized to determine two novel mutations in the mitochondrial genome: "A 21-year-old woman who has been suspected of mitochondrial cytopathy, but negative for common mitochondrial DNA (mtDNA) point mutations and deletions, was screened for unknown mutations in the entire mitochondrial genome by temperature gradient gel electrophoresis". p53 mutation in pancreatic secretions Lohr and coworkers (2001) report that in a comprehensive study of pancreatic secretions of individuals without pancreatic carcinoma, p53 mutations could be found in the pancreatic juices of a small percentage of participants. Because mutations of p53 has been extensively found in pancreatic carcinomas, the researchers for this investigation were attempting to determine if the mutation itself can be linked to the development of pancreatic cancer. While Lohr was able to find p53 mutations via TGGE in a few subjects, none subsequently developed pancreatic carcinoma. Thus, the researchers conclude by noting that the p53 mutation may not be the sole indicator of pancreatic carcinoma oncogenesis. Microbial ecology DGGE of small ribosomal subunit coding genes was first described by Gerard Muyzer, while he was Post-doc at Leiden University, and has become a widely used technique in microbial ecology. PCR amplification of DNA extracted from mixed microbial communities with PCR primers specific for 16S rRNA gene fragments of bacteria and archaea, and 18S rRNA gene fragments of eukaryotes results in mixtures of PCR products. Because these