DNA sequencing is the process of determining the order of base pairs in a section of DNA. Two early methods were Maxam-Gilbert sequencing developed in 1976-1977 which used chemical modification, and chain termination which used single-stranded DNA, primers, polymerase, and nucleotides in four reactions to terminate elongation. Newer dye-terminator methods use fluorescent dyes on chain terminators to sequence in a single reaction. DNA sequencing can help diagnose disease, identify crime suspects, and was used in the Human Genome Project to map the 20,000-25,000 human genes.