pression can be divided into to two stages, transcription and translation, the first producing an RNA copy of the genes and the second resulting in synthesis of a protein whose amino acid sequence is determined via the genetic code, by the nucleotide sequence of the RNA transcript. It must be noted however that this simplified description, should not result in attention being drawn away from the key points in the gene expression pathway at which information flow is regulated.A complete copy of the genome must be made every time a cell divides. DNA replication has to be extremely accurate in order to avoid the introduction of mutations into the genome copies. Some mutations do, however occur, either as errors in replication or due to the effects of chemical and physical mutagens that direcly alter the physical structure of DNA. DNA repair enzymes correct many of these errors; those that escape the repair processes become permanent features of the lineage descending from the original mutated genome. These events, along with genome rearrangements resulting from recombination, underlie molecular evolution, the driving force behind the evolution of living organisms.Of all the genomes in existence our own is quite naturally the one that interests us the most. An overview of it’s structure is therefore necessary, in commanding a picture of the goals trying to be achieved by the human genome project, and therefore the technologies developed in trying to obtain them.The human genome is made up of two distinct components. The nuclear genome, which comprises approximately 3 000000000 bp (base pairs) of DNA. The nuclear genome is divided into 24 linear DNA molecules, the shortest is 55 Mb in length and the longest 250 Mb, each contained in a different chromosome. These 24 chromosomes consist of 22 autosomes and the two sex shromosomes, X and Y. The human genome also consists of the mitochondrial genome, a circular DNA molecule of 16, 569 bp, ...
