Genomic Analysis

In prokaryotes and viruses, genomic analysis is vastly simplified because the genomes consist of comparatively small single chromosomes with a considerably reduced complexity of gene organisation. Prokaryote genes consist of uninterrupted arrays of amino acid coding sequences that extend from the start site to the finish of the coding region with relatively little intergenic non-coding DNA. In eukaryotes the position is more complex: the DNA is arranged into several chromosomes and typical
genes are not continuous stretches of coding sequence but rather are broken up into exons, which encode amino acids and non-coding introns.
The first genome sequence to be completed was that of the virus-like bacteriophage PhiX174 reported by Sanger and colleagues in 1977. PhiX174 consisted of approximately 5375 nucleotides and 11 genes with no intergenic or intronic sequences. The publication of the PhiX174 sequence predated the publication of the full sequence of the human genome by some 25 years. Sanger’s key discovery of the ‘chain termination’ DNA sequencing method enabled the nucleotide base order to be read in comparatively long stretches of DNA. This is the basis for modern DNA sequencing, which led to the development of the highthroughput protocols that allowed the completion the draft human genome sequence in 2001