A sexual difference in the chromosomes of two species of agamid lizards

Abstract

The diploid number of chromosomes in Calotes versicolor is 34 in the male and 33 in the female. The numerical difference in the two sexes is based on the condition of the sex chromosome; in the male it is present as a homologous pair, while in the female it remains unpaired. The sex chromosome was identified as one of the micro-chromosomes (the chromosome No. 7) in this species. Sitana ponticeriana possesses the diploid number of 46 in the male and 45 in the female. The sex chromosome identified in this form is also one of the micro-chromosomes (chromosome No. 13), which has no partner in the female, whereas in the male it is in the paired state having a homologous mate. It was established therefore that, in both species studied, the female is heterogametic as regards the sex chromosome. The chromosome complement of Calotes versicolor consists of 12 V-shaped macro-chromosomes and 22 dot-like micro-chromosomes, while in Sitana ponticeriana there are 24 rod-shaped macro-chromosomes and 22 dot-like micro-chromosomes. The difference in the karyotypes of these two species can be accounted for on the basis of the formation of V-shaped multiple chromosomes by means of the fusion of two rods at the point of fibre attachment. The karyological relationships in the Family Agamidae were discussed. The chromosome number previously reported for Uromastix hardwicki was found to be erroneous; the diploid number in this species is 34.