PCR was developed in 1985 by Kary B. Mullis, who was awarded the 1993 Nobel Prize in chemistry for his work. It is used in DNA fingerprinting and in medical tests to identify diseases from the infectious agent's DNA. In forensic use, the test can be used to compare two samples of DNA, usually by looking at matches (or mismatches) of six inherited traits (e.g., hair curliness) from each of the samples. Each trait is controlled by a single gene, each gene having at least two forms, or alleles, resulting in 21 combinations of these alleles, some of them very rare. A nonmatch conclusively excludes a suspect. PCR also is used in taxonomic classification to help show evolutionary relationships between organisms on the molecular level. It has the advantage of being able to be used even when only very small samples, such as tiny pieces of preserved tissue from extinct animals, are available.