The project with the goal of sequencing the human genome, which is the collection of all human genes. In the 1990s, a scientific commitment was made to identify all the genes in human chromosomes, and some other organelles such as mitochondrion. This involved international cooperation and a very significant effort by many laboratories. Genes are made of DNA, which is composed of sequences of four different nucleotides, with perhaps as many as three billion nucleotides total in the genome. The genome project's goal is to determine all the nucleotides and their sequence, and then make this information available through the Internet. A gene is a functional segment of this DNA sequence that produces a product, an mRNA, which in turn guides the formation of a protein. Estimates of the number of genes in humans vary widely, with the averages falling in the range of 70,000 to perhaps 120,000. It is believed that identifying the genome sequence is the first step necessary for producing dramatic advances in biology and medicine. In addition to the human genome project, there are similar on-going projects attempting to sequence the genomes of other organisms as well.