An extraordinarily low diploid chromosome number in the reptile Gonatodes taniae (Squamata, Gekkonidae).

Mitotic and meiotic chromosomes of the gekkonid lizard Gonatodes tanieae from Venezuela were analyzed with conventional staining, differential banding techniques, and in situ hybridization using a synthetic telomeric DNA probe. The karyotype of this species is distinguished by the extraordinarily reduced diploid chromosome number of 2n = 16, which is the lowest value known for reptiles. In contrast to most other reptilian species, G. taniae has exclusively bi-armed (meta- and submetacentric) macrochromosomes and no microchromosomes. Examination of the mitotic chromosomes with AT and GC base pair-specific fluorochromes shows the absence of multiple banding patterns in euchromatic regions. The n = 8 diakinetic bivalents of male meiosis present terminal, subterminal, interstitial, and pericentromeric chiasmata. Comparison of the karyotypes of G. taniae and G. vittatus (also collected in Venezuela), and with those of three other Gonatodes species, indicates that the exceptional diploid number of 2n = 16 is the result of repeated centric fusions. In addition to the telomeres, all pericentromeric regions of the G. taniae chromosomes contain considerable amounts of the (TTAGGG)n telomeric sequence. These are probably not only relics of the centric fusions, but also a major component of the highly repetitive DNA in the C band-positive heterochromatin.