The Human Genome Project (HGP), according to the National Human Genome Research Institute, was the international, collaborative research program formed to complete the mapping and understanding of all the genes of human beings. All our genes together are known as our "genome." The hereditary material is the double helix of deoxyribonucleic acid (DNA), which contains all human genes. DNA, in turn, is made up of four chemical bases, pairs of which form the "rungs" of the twisted, ladder-shaped DNA molecules. All genes are made up of stretches of these four bases, arranged in different ways and in different lengths. During the HGP, researchers deciphered the human genome in three major ways: determining the order, or "sequence," of all the bases in our genome's DNA; making maps that show the locations of genes for major sections of all our chromosomes; and producing what are called linkage maps through which inherited traits (such as those for genetic disease) can be tracked over generations. The HGP revealed that there are probably somewhere between 30,000 and 40,000 human genes. The completed human sequence can now identify their locations. The result of the HGP has given the world a resource of detailed information about the structure, organization, and function of the complete set of human genes. This information can be thought of as the basic set of inheritable "instructions" for the development and function of a human being. The International Human Genome Sequencing Consortium completed and published the full sequence in April 2003.