Genetic modification. Conceptual illustration of a DNA (deoxyribonucleic acid) molecule (represented as a monument) with scaffolding for maintenance and repair. This could represent the repair of damaged DNA (such as in radiation-induced mutations or inherited disease), the maintenance of healthy DNA to prevent ageing-related diseases, or the modification of DNA. This last application is called genetic engineering. DNA is a long, helical molecule. Two intertwining strands are linked by the nucleotide bases on the strands (the horizontal struts). The sequence of these nucleotide bases forms the genetic code.