A computer program integrates the data from individual sequencing reactions. It can spot where DNA fragments overlap and order them as they originally were on the chromosome. Many overlapping sequences reads are needed to generate the uninterrupted sequence of the original stretch of DNA. During the Human Genome Project, every base pair of DNA was sequenced an average of nine times. Some stretches of DNA were easy to read and needed to be sequenced little less often, while other stretches were more difficult to read and had to be sequenced more often. During the Human Genome Project scientists ran more than 50 million sequencing reactions. Some 2000 scientists from more than two dozen labs around the world, worked on the project.