ABSTRACT
DNA is composed of several different chemical units: a deoxyribose sugar unit, phosphate group, and one of four different nucleotide bases (adenine [A], guanine [G], cytosine [C], or thymine [T]). At the molecular level, it is the order of these bases that carries the code to build proteins within the cell that inevitably control the function of various cells and also determine an organism’s physical characteristics. In the human genome, the 23 pairs of chromosomes contain 3 billion bases. The length of the chromosomes
(in base pairs) varies greatly, with the smallest chromosome containing 50 million bases (chromosome Y) and the longest containing 250 million bases (chromosome 1). It is the primary function of DNA sequencing to determine the order of these nucleotide bases.
