The genetic material (DNA) of living organisms is structurally the same whether it is found in humans, plants, fungi or bacteria. This fact enables the genetic engineer to use molecular genetic techniques to transfer genes from one species to another and so produce, for example, transgenic cotton plants expressing bacterial genes for novel characteristics such as herbicide and insect resistance. This fact also makes it possible to universally employ related techniques to help in the genetic identification of individual people, varieties or strains in human, plant or microbial populations. Thus, the methods used in the compilation of human genetic fingerprints for the identification of people in immigration, forensic and criminal cases could equally be used to differentiate between plant species, cultivars and progeny in plant breeding programs, to identify the particular pathogen strain in an outbreak of plant disease, or to characterise the varieties of mycorrhizal fungi in an agricultural field. The sensitivity of such techniques rests in their ability to detect the rare or subtle differences that exist between the genes of one individual and another.