EVOLUÇÃO CARIOTÍPICA DE SERPENTES REVISITADA

Abstract

Karyotype evolution of snakes revisited. Cytogenetic analyzes have proved been valuable tool for characterization, evolutionary mechanisms and phylogenetic relationships in several species. Most of cytogenetic studies on snakes are restricted to analyzes of chromosome number and morphology. Despite this, a chromosomal characterization, is important for heterochromatin analysis and / or chromosomal location of specific sequences, such as DNA and telomeric and has contributed significantly to the studies of systematics and phylogeny in various groups of snakes. This work aimed to perform a literature review of the cytogenetics studies of snakes, aiming to provide subsets for a better understanding of the theme. The snakes present a bimodal karyotype, with presence of macrochromosomes and microchromosomes. The diploid number within the group ranges from 2n = 24 to 2n = 50, where 2n = 36 is considered the common karyotype and is present in most species. Despite being considered conserved in relation to the diploid number, the snakes karyotype has shown the difference in the pattern of distribution of bands and specific sequences as the DNAr and telomeric regions. The main mechanism of chromosome evolution within the group is given by events involving centric fusions and fissions. The pattern of heterochromatin distribution has been shown to be an important cytotaxonomic marker within families. The differentiation of ZZ / ZW or multiple sex chromosomes occurs in more derived species where there are few or no cases of heteromorphism in basal lines.