These fluorescently-labeled DNA fragments are then separated by size in a process called electrophoresis. Incorporation of a dideoxynucleotide occurs at random, resulting in multiple copies of the DNA template, all different lengths. Each dideoxynucleotide has a unique fluorescent “tag” that allows A, T, C, and G to be clearly identified. When one is incorporated into a growing copy of DNA sequence, no other nucleotide can be added onto the chain after it. Sanger sequencing relies on chemicals called dideoxynucleotides, which are also known as ‘chain terminating’ nucleotides. While methods for DNA sequencing have evolved over the years, the technique generally consists of breaking long strands of DNA into many small pieces, using one of several types of tests to determine the order of the nucleotide bases that make up those pieces, and then reassembling the data back in the order of the original DNA strand.ĭeveloped in the 1970’s, this is the method that was used in the Human Genome Project from 1990-2003 to completely sequence the DNA of a human for the first time. The information contained within these genes allows our cells to produce an enormous variety of proteins that serve as the building blocks for our bodies and that govern how the body works. There are approximately 20,000 genes in the human genome.

The information contained in the RNA is then often translated by tiny molecular machines into proteins. Specific segments of DNA called genes serve as templates to make (transcribe) RNA. The base, sugar, and phosphate form a unit called a nucleotide, which is referred to by the base (A, C, T, or G) it contains. These bases are bonded at the sides of the ladder to a sugar and phosphate, which form the vertical backbone of the DNA double helix (the “sides” of the ladder). Because of their shape, adenine always pairs with thymine and guanine always pairs with cytosine to form a complete rung. These rungs are created from two of four possible bases: adenine (A), cytosine (C), guanine (G), and thymine (T). It is structured like a twisted ladder, with two sides and rungs made up of two pieces that fit together. DNA is the unique genetic code found in most cells in humans as well as in organisms such as bacteria, many viruses, parasites, and plants.

Gene sequence definition