<P> It was far too expensive at that time to think of sequencing patients' whole genomes . So the National Institutes of Health embraced the idea for a "shortcut", which was to look just at sites on the genome where many people have a variant DNA unit . The theory behind the shortcut was that, since the major diseases are common, so too would be the genetic variants that caused them . Natural selection keeps the human genome free of variants that damage health before children are grown, the theory held, but fails against variants that strike later in life, allowing them to become quite common . (In 2002 the National Institutes of Health started a $138 million project called the HapMap to catalog the common variants in European, East Asian and African genomes .) </P> <P> The genome was broken into smaller pieces; approximately 150,000 base pairs in length . These pieces were then ligated into a type of vector known as "bacterial artificial chromosomes", or BACs, which are derived from bacterial chromosomes which have been genetically engineered . The vectors containing the genes can be inserted into bacteria where they are copied by the bacterial DNA replication machinery . Each of these pieces was then sequenced separately as a small "shotgun" project and then assembled . The larger, 150,000 base pairs go together to create chromosomes . This is known as the "hierarchical shotgun" approach, because the genome is first broken into relatively large chunks, which are then mapped to chromosomes before being selected for sequencing . </P> <P> Funding came from the US government through the National Institutes of Health in the United States, and a UK charity organization, the Wellcome Trust, as well as numerous other groups from around the world . The funding supported a number of large sequencing centers including those at Whitehead Institute, the Sanger Centre, Washington University in St. Louis, and Baylor College of Medicine . </P> <P> The United Nations Educational, Scientific and Cultural Organization (UNESCO) served as an important channel for the involvement of developing countries in the Human Genome Project . </P>

Where did scientists obtain human dna for analysis in the human genome project