Cytogenetically Elusive Sex Chromosomes in Scincoidean Lizards

Abstract

The lizards of the species-rich clade Scincoidea including cordylids, gerrhosaurids, skinks, and xantusiids, show an almost cosmopolitan geographical distribution and a remarkable ecological and morphological divergence. However, previous studies revealed limited variability in cytogenetic traits. The sex determination mode was revealed only in a handful of gerrhosaurid, skink, and xantusiid species, which demonstrated either ZZ/ZW or XX/XY sex chromosomes. In this study, we explored the karyotypes of six species of skinks, two species of cordylids, and one gerrhosaurid. We applied conventional and molecular cytogenetic methods, including C-banding, fluorescence in situ hybridization with probes specific for telomeric motifs and rDNA loci, and comparative genomic hybridization. The diploid chromosome numbers are rather conserved among these species, but the chromosome morphology, the presence of interstitial telomeric sequences, and the topology of rDNA loci vary significantly. Notably, XX/XY sex chromosomes were identified only in Tiliqua scincoides, where, in contrast to the X chromosome, the Y chromosome lacks accumulations of rDNA loci. We confirm that within the lizards of the scincoidean clade, sex chromosomes remained in a generally poor stage of differentiation.

Cytogenetic Analysis of the Members of the Snake Genera Cylindrophis, Eryx, Python, and Tropidophis

“…Poorly differentiated sex chromosomes are more prone to turnovers than highly differentiated sex chromosomes [ 73 ], which can—together with differences in lineage ages—explain the emerging pattern of the higher variability in sex chromosome systems in snakes from the scolecophidian and henophidian groups compared with the evolutionary stable ZZ/ZW sex chromosomes of caenophidian snakes [ 14 , 16 , 24 , 27 ]. Molecular methods such as RAD-seq or whole-genome coverage analyses have been successful in uncovering sex determination systems not only in snakes but also in other squamate lineages with poorly differentiated sex chromosomes [ 27 , 74 , 75 , 76 ], and might offer a way to resolve sex determination systems in scolecophidian and henophidian snakes in the future.…”

A Fish of Multiple Faces, Which Show Us Enigmatic and Incredible Phenomena in Nature: Biology and Cytogenetics of the Genus Carassius

“…The FISH method, in which rDNA probes are hybridized on chromosomal DNA, reveals exact chromosomal positions where the rDNAs are situated. Regions containing rDNA can be easily amplified using PCR and labeled with specific nucleotides using labeling PCR [ 64 ] or nick translation [ 65 ]. These regions encoding rRNA are arranged into tandemly repeated units: major 45S locus composed of 18S , 5.8S , and 28S genes, and minor 5S locus, is formed independently.…”

A Fish of Multiple Faces, which Show us Enigmatic and Incredible Phenomena in Nature: Biology and Cytogenetics of the Genus Carassius

“…The FISH method, in which rDNA probes are hybridized on chromosomal DNA, reveals exact chromosomal positions where the rDNAs are situated. Ribosomal DNA regions can be easily amplified using PCR and labelled with specific nucleotides using labelling PCR [62] or nick translation [63]. These regions encoding rRNA are arranged into tandemly repeated units: major 45S unit composed of 18S, 5.8S, and 28S genes, and minor 5S unit which forms independently.…”