Polymorphism of the Microchromosomes and the Nucleolar Organizer Region in Pristidactylus achalensis (Sauria: Iguanidae)

The chromosomes of 39 specimens of the lizard Pristidactylus achalensis were analyzed, and a karyotype of 12 biarmed macrochromosomes and 24 microchromosomes was determined. With regard to the microchromosomes, the animals grouped in three types: (a) with two microchromosomes evidently larger than the rest, (b) with one evidently larger microchromosome, and (c) with no evidently larger microchromosomes. Males of the three types showed six macro- and 12 microassociations in meiocytes. The existence of a dimorphic microchromosome due to the addition (or deletion) of heterochromatic material is compatible with these results. In testicular preparations, 21.9% of the mitotic figures and 5.9% of cells in diakinesis-metaphase I were apparently polyploid. The origin of these cells is discussed. Four of the animals presented only one secondary constriction and only one positive region in Ag-stained preparations, suggesting a deletion of the nucleolar organizer region.