These genes need to be removed, as far as possible, usually by back-crossing. The nature of crop growing seasons, or animal generation times, means that the process is slow. Genetic engineering extends the available pool of genes and speeds up the process. Genetic engineering depends upon the ability to identify and manipulate specific genes. There are around 100,000 genes in a mammal.
Genetic engineering can involve moving genes both within or between species.
It is the movement of genes between species which is of the greatest concern. Organisms modified in this way, are referred to as being transgenic or genetically modified or simply as GMOs. GMO technology thus gives the ability to add, subtract, alter or exchange an individual gene or a group of genes, which are known to influence an individual characteristic. A single specific change can then be made to a tried and tested variety of a given species. In contrast to conventional breeding, genetic engineering does not involve the mixing of the entire gene complement of two individuals, and the then subsequent need to re-sort them to give only the desired change.