Occurrence of B chromosomes in lizards: a review.

Although B chromosomes have been reported in many species of plants and animals, few studies have revealed the presence of these extra chromosomes in lizards. B chromosomes of lizards show different morphologies and sizes, from microchromosomes to macrochromosomes, or elements of intermediate size between smaller and larger A chromosomes, and number variability at intra- and inter-individual levels. In most cases, they are late-replicating and show either heterochromatic or no distinctive patterns after C-banding. The great majority of the publications about supernumerary chromosomes in this group have been based on conventional staining analyses, and there is no study designed to address questions related to their composition and structure or origin and evolution.

Chromosomal studies on sphaerodactyl lizards of genera Gonatodes and Coleodactylus (Squamata, Gekkonidae) using differential staining and fragile sites analyses.

The karyotypes of three species of sphaerodactyl gekkonid lizards are described after conventional and differential staining. Karyotypes of Gonatodeshumeralis and G. hasemani are formed by a gradual series of 32 acrocentric chromosomes, similar to those already published for other species of the genus. G. humeralis shows multiple Ag-NORs with intra-individual variability, and positive C-bands located at centromeric and telomeric regions of several chromosome pairs. Coleodactylus amazonicus, the first non-Gonatodes sphaerodactyl studied so far karyologically, exhibits 36 acrocentric/subtelocentric chromosomes and a single pair of Ag- NORs. Fragile sites were detected on two medium-sized chromosome pairs in the karyotype of G. humeralis, most of them obtained in BrdU-treated culture preparations. These sites may represent a putative fission/fusion spot involved in the differentiation of G. humeralis-like 2n = 32 and C. amazonicus-like 2n = 36 karyotypes. Our results, especially on the location of Ag-NORs and the description of fragile sites, are relevant in improving our knowledge about the events of chromosome evolution in this extremely variable and poorly known group of lizards.