The vaccine for the Hepatitis B virus is made by cloning the gene for a protein of the virus into bacteria, isolating that protein from the bacteria, and using it as a vaccine. Of course, toxic materials may also be made this way, but it is usually easier to kill people with bullets or poison chemicals than to use fancy biological agents. It is often possible to tell whether an individual has a certain gene, using one of several techniques. In several cases, this has aided police in solving crimes. People often confess, faced with DNA evidence, although the labs which do the DNA analyses must be extraordinarily careful not to contaminate the samples.
Gene therapy is a possibility for the future, though it has already been tried without sure success.
Several tumor-suppressor genes have now been located. These genes, in normal form, suppress the formation of cancerous tumors of certain types. If a person is heterozygous or homozygous for defective forms of the gene, the person generally has a very high chance of getting cancer early in life.