Several reports have been published since the 1990s on the genetic makeup of the Siberian tiger and its relationship to other subspecies. One of the most important outcomes has been the discovery of low genetic variability in the wild Far Eastern population, especially when it comes to maternal or mitochondrial (mtDNA) lineages. It seems that a single mtDNA haplotype almost completely dominates the maternal lineages of wild Siberian tigers. On the other hand, captive cats appear to show higher mtDNA diversity. This may suggest that the subspecies has experienced a very recent genetic bottleneck caused by human pressure, with the founders of the captive population being captured when genetic variability was higher in the wild. However, it may well be that the Siberian tiger population has always shown relatively low genetic diversity, due to a small number of founders colonising the Far East. Work with the preserved remains of the now extinct Caspian Tiger (P.t. virgata) has shown that the two subspecies share a comparatively recent common history, at least when it comes to mtDNA lineages. It appears that tigers colonised central Asia at most 10,000 years ago, and the modern Siberian stock may be the result of a few Caspian tigers subsequently wandering east via northern Asia.
New genetic analysis revealed that the extinct Caspian tiger lives on in the Siberian Tiger. Researchers from the University of Oxford in the United Kingdom collected tissue samples from 20 Caspian tiger specimens kept in museums across Eurasia. Afterwards, researchers from the U.S. National Cancer Institute (NCI) Laboratory of Genomic Diversity in Frederick, Maryland, sequenced parts of five mitochondrial genes. The Caspian Tiger's mitochondrial DNA is only one letter of genetic code separated from Siberian Tiger DNA, while it is readily distinguishable from the DNA of other tiger subspecies. This indicates that the Caspian and the Siberian subspecies are really one. The scientists have concluded that the two are so similar because both were descended from the same migrating ancestor. The ancestor colonized Central Asia via the narrow Gansu Corridor (Silk Road) from eastern China. The researchers suggest that through the early 1900s, Caspian and Siberian tiger populations intermingled, but hunters subsequently isolated the two groups. This resulted in the Siberian population splitting off from the Caspian population only in the past century.