Comparative cytogenetics and the determination of primitive karyotypes

Skinks represent the most diversified squamate reptiles with a great variation in body size and form, and are found worldwide in a variety of habitats. Their remarkable diversification has been accompanied by only a few chromosome rearrangements, resulting in highly-conservative chromosomal complements of these lizards. In this study cross-species chromosome painting using Scincus scincus (2n = 32) as the source genome, was used to detect the chromosomal rearrangements and homologies between the following skinks: Chalcides chalcides (2n = 28), C. ocellatus (2n = 28), Eumeces schneideri (2n = 32), Lepidothyris fernandi (2n = 30), Mabuya quinquetaeniata (2n = 32). The results of this study confirmed a high degree of chromosome conservation between these species. The main rearrangements in the studied skinks involve chromosomes 3, 5, 6 and 7 of S. scincus. These subtelocentric chromosomes are homologous to the p and q arms of metacentric pair 3 and 4 in C. chalcides, C. ocellatus, L. fernandi, and M. quinquetaeniata, while they are entirely conserved in E. schneideri. Other rearrangements involve S. scincus 11 in L. fernandi and M. quinquetaeniata, supporting the monophyly of Lygosominae, and one of the chromosomes S. scincus 12–16, in M. quinquetaeniata. In conclusion, our data support the monophyly of Scincidae and confirm that Scincus-Eumeces plus Chalcides do not form a monophyletic clade, suggesting that the Scincus-Eumeces clade is basal to other members of this family. This study represents the first time the whole genome of any reptile species has been used for cross-species chromosome painting to assess chromosomal evolution in this group of vertebrates.

Section: Discussionmentioning

confidence: 99%

Skinks (Reptilia: Scincidae) Have Highly Conserved Karyotypes as Revealed by Chromosome Painting

Giovannotti

Caputo²,

O’Brien³

et al. 2009

“…The phylogenetic analysis of the observed pattern is complicated by the lack of additional data from other populations and by difficulties in finding an appropriate outgroup. Comparative cytogenetics should attempt to use the outgroup method to determine the primitive and derived state of chromosome rearrangements (Qumsiyeh and Baker, 1988). The choice of an appropriate outgroup, usually representing a closely related taxon, is fraught with difficulty in the case of Calomyscus.…”

Section: Discussionmentioning

confidence: 99%

Comparative cytogenetics of hamsters of the genus <i>Calomyscus</i>

Graphodatsky

Sablina²,

Meyer³

et al. 2000

Karyotypes of Calomyscus from different regions of Turkmenistan, Iran, and Azerbaijan were studied using chromosome banding (G- and C-banding) and analyses of meiosis in laboratory hybrids. Extensive variation in the diploid number and the number of autosomal arms (FNa) was revealed (2n = 30, FNa = 44; 2n = 32, FNa = 42; 2n = 44, FNa = 46; 2n = 44, FNa = 58; 2n = 37, FNa = 44; 2n = 50, FNa = 50; 2n = 52, FNa = 56). Centric and tandem fusions and heterochromatin changes were identified as the major modes of karyotype evolution in this group. Natural hybrids between individuals with different karyotypes were recorded, and regular chromosome pairing in meiosis was observed in laboratory hybrids. Fluorescence in situ hybridization with a 353-bp BspRI complex tandem repeat indicated that chromosomal repatterning occurred recently within the genus. There is no unequivocal evidence suggesting the role of chromosomal change in the speciation of the populations of Calomyscus examined.

“…If chromo somal banding and gene mapping data are adequate in various species, the number and types of chromosomal rearrangements incorporated in the lineage can be inferred. By extension, such studies will allow us to describe karyotype evolution and conse quently to determine primitive karyotypes and gene maps (Qumsiyeh and Baker, 1988).…”

mentioning

confidence: 99%

Chromosome banding and gene localizations support extensive conservation of chromosome structure between cattle and sheep

Hediger

Ansari

Stranzinger³

1991

By using three gene probes, one derived from the porcine major histocompatibility complex (MHC) and two from bovine cytokeratin genes, type I (KRTA) and type II (KRTB), the hypothesis of conservation of genome structure in two members of the family Bovidae was examined. Gene mapping data revealed the MHC to be in chromosome region 23q15→q23 in cattle (BOLA) and 20q15→q23 in sheep (OLA). KRTA was localized to chromosome region 19q25→q29 in cattle and 11q25→q29 in sheep and KRTB to 5q14→q22 in cattle and 3q14→q22 in sheep. The banding patterns of the chromosome arms to which the loci were assigned were identical in both species. Moreover, the resemblances of GTG- or QFQ-banding patterns between the cattle and sheep karyotypes illustrated further chromosome homologies. These studies, based on gene mapping comparisons and comparative cytogenetics, document that within bovid chromosomes, homology of banding patterns corresponds to a homologous genetic structure. Hence, we propose that gene assignments on identified chromosomal segments in one species of the Bovidae can be extrapolated, in general, to other bovid species based on the banding homologies presented here.