genetic engineering been produced by transfer of antigencoding genes to bacteria. Genes have been introduced to crop plants for various reasons, for instance to reduce damage during harvest or to make them resistant to the herbicides used in controlling weeds. Genetically modified tomatoes and soya beans are now widely available. There is also hope that in future many genetic diseases will be treatable by manipulating the faulty genes responsible. However, ge-
in its new environment and is regulated correctly and predictably. Initial successes in DNA transfer were achieved with bacteria and yeast. Human genes coding for medically useful proteins have been transferred to bacteria. Human insulin, growth hormone, and interferon are now among a wide range of therapeutic substances produced commercially from genetically engineered bacteria. Genetically engineered vaccines have also
Genetic code
95