The function of genes, known since the work of Beadle and Tatum in 1945 and Linus Pauli is to code for the structure of proteins (more accurately, polypeptide chains). The discipli biochemistry and genetics are united in theDNA nucleotide sequence of a gene coding for acid sequence of a polypeptide chain. The latter sequence determines not only how a prot into three dimensions but also the specific enzymatic reaction (s) or other chemical role(s) protein in the organism. A considerable body of effort over the past 50 years consisted of which proteins were coded by which genes. Starting with an isolated protein, the amino sequence was used to predict the nucleotide coding sequence. Eventually, an oligonucle with this sequence could be made and used by hybridization to isolate or locate the chrom gene. Starting with a mutant gene in an organism, biochemical assays are used to determin which protein is aberrant, or mapping studies are used to determine