A subspecies is a genetically distinct population within a species that has some phenotypic differences from the rest of the species, but is not yet reproductively isolated. Nine subspecies of the tiger, Panthera tigris, have been identified. Six of these subspecies are found on mainland Asia. Three of the subspecies originate from the Sunda Islands. These islands include Bali, Java and the large island of Sumatra. [Figure 3.1] shows these three islands. The Bali tiger, Panthera tigris balica (P. t. balica), became extinct in the 20th Century. The Bali tiger was found only on the island of Bali. The Javan tiger, P. t. sondaica, became extinct in the 20th Century. The Javan tiger was found only on the island of Java. The Sumatran tiger, P. t. sumatrae, lives only on Sumatra and is the closest living relative of Bali and Javan tigers. 20000 years ago land bridges temporarily connected the Sunda Islands. A recent study carried out a genetic analysis of the nine subspecies of tiger. Specific sections of mitochondrial DNA (mtDNA) that are useful in studies of evolution were amplified using PCR and compared to assess their evolutionary history. The source of DNA for the extinct subspecies came from museum specimens. mtDNA was extracted and polymerase chain reaction (PCR) carried out using primers based on specific sections of tiger mtDNA. The mtDNA sections for the three island subspecies were genetically distinct from the other six mainland subspecies. The mtDNA sections for the three island subspecies were all found to be very similar.