The human genome has been estimated to have 20,000 - 25,000 human protein - coding genes. Before it was thought that the number of genes in the human genome was about 100,000, but with better and more advanced gene finding technology, this number has been revised down to the current estimate, and could continue to drop further. The human genome has 23 chromosome pairs with a total of about 3 billion DNA base pairs. There are 22 autosomal chromosomes plus the sex determining X and Y chromosomes, to make 23 pairs.