The sequencing of the entire genome of an organism.
The technique that allows researchers to read and decipher the genetic information found in the DNA of anything from bacteria to plants to animals is called genomic sequencing. Once a tedious, painstaking process, today, thanks to new techniques and the advent of powerful computers, it has been sped up a hundredfold. Sequencing involves determining the order of bases, the nucleotide subunits (adenine, guanine, cytosine and thymine, referred to by the letters A, G, C and T) found in DNA. (Humans have about 3 billion base pairs.) Three nucleotides in a row specify one kind of amino acid, and a gene is defined by a long string of these triplets. There are various techniques to read the sequence of these letters in genes and genomes. So-called shotgun sequencing was used to help decode the human genome. Using this method, the DNA to be sequenced is first broken apart with enzymes, since gene-sequencing machines can only handle small stretches of DNA at a time. Once these random fragments are sequenced, powerful supercomputers compare overlapping sections and recreate the original, long strand. By decoding genomes and sequencing genes, researchers are beginning to understand how those strings of letters work together to create a living organism.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.