Human genome research. Rows of GeneAmp polymerase chain reaction (PCR) systems copying human DNA at the Joint Genome Institute (JGI). The JGI is part of the international Human Genome Project (HUGO) that aims to map the whole human genome, the three billion base pairs that form the genetic code of human DNA (deoxyribonucleic acid), by 2003. PCR produces exact copies of DNA fragments, as polyme- rase enzymes make single DNA strands synthesize mirror copies of themselves. Repeating the process produces vast numbers of cloned fragments for analysis. The JGI, in Walnut Creek, California, is a collaboration between three of the US Department of Energy's National Laboratories.