Standardized Karyotype and Idiogram of Bengal Monitor Lizard, Varanus bengalensis (Squamata, Varanidae)

The standardized karyotype and idiogram of the Bengal monitor lizard (Varanus bengalensis) from the Kalasin Province of Thailand were studied. Blood samples were taken from male and female lizards. The standard T-lymphocyte cell was cultured at 26°C for 96 h. The mitotic chromosomes were harvested by colchicine-hypotonic-fixation-air drying technique. Conventional staining, Ag-NOR banding and C-banding techniques were applied to stain the chromosome with 20% Giemsa’s solution. The results showed that the number of diploid chromosome was 2n=40, while the fundamental number (NF) was 54 in males and 55 in females. The types of macrochromosomes were 4 large metacentric, 4 small metacentric, 6 small submetacentric, 2 small telocentric macrochromosomes and 24 microchromosomes. The Z chromosome is the small telocentric chromosome, while the W chromosome is the small metacentric chromosome. In addition, the short arm pericentromeric region of chromosome pair 1 showed clearly observable nucleolar organizer regions (NORs). This data is the first report on polymorphism of NORs in V. bengalensis. The result showed that the heteromorphic of one male had a different size of NORs of chromosome pair 1 (1a1b), while one female had an equal size of both chromosome pair 1 with a homomorphic (1a1a). The karyotype formula is as follows: