Karyotype description and evidence of multiple sex chromosome system X1X1X2X2/X1X2Y in Potamotrygon aff. motoro and P. falkneri (Chondrichthyes: Potamotrygonidae) in the upper Paraná River basin, Brazil

Abstract

Cytogenetic analysis of Potamotrygon aff. motoro and P. falkneri indicated the occurrence of an X1X1X2X2/X1X2 Y multiple sex chromosome system in both species, with 2n = 66 chromosomes for females and 2n = 65 chromosomes for males. The nucleolus organizer regions (NORs) identified using Ag-NOR technique showed that both species have multiple Ag-NORs (5 to 7 chromosomes stained). C-banding technique indicated the presence of heterochromatic blocks in the centromeric regions of almost all chromosomes in both species. Through this study there was evidence of heterogeneity in the karyotypes, which suggests that chromosomal rearrangements such as inversions and/or translocations occurred during the chromosomal evolution in two species of this genus.<br>Análises citogenéticas de Potamotrygon aff. motoro e P. falkneri identificaram a ocorrência de um sistema múltiplo de cromossomos sexuais do tipo X1X1X2X2/X1X2Y, em ambas as espécies, com 2n = 66 cromossomos em fêmeas e 2n = 65 cromossomos nos machos. As regiões organizadoras de nucléolos (RONs) identificadas pela reação Ag-RON, evidenciaram marcações múltiplas em ambas as espécies (com variações de 5 a 7 RONs). A técnica de bandamento C, revelou a presença de blocos heterocromáticos localizados nas regiões centromérica em quase todos os cromossomos nas duas espécies em estudo. Através do presente estudo foi evidenciada uma heterogeneidade nos cariótipos, permitindo sugerir que rearranjos cromossômicos, como inversões e/ou translocações, ocorreram durante a evolução cromossômica nas duas espécies desse gênero

Characterization and description of a multiple sex chromosome system in Potamotrygon motoro (Chondrichthyes, Myliobatiformes) from the Paraná River, Argentina

“…These facts support the phylogenetic classifications proposed by several authors, whereby the Potamotrygonidae family is included in the Myliobatiformes (Mould, 1997;Carvalho et al, 2004;Martin, 2004;Menni, 2004). However, in the species studied of the family Potamotrygonidae, multiple NORs and a pericentromeric C-band pattern are shared as cytogenetic markers (de Valentim et al, 2006;Cruz et al, 2011).…”

“…Furthermore, other rearrangements may have arisen through deletions and inversions. Cruz et al (2011) reported the presence of heteromorphic sex chromosomes in P. aff. motoro and P. falkneri, both of which have 2n = 66 chromosomes in the females and 2n = 65 chromosomes in the males.…”

“…However, the occurrence of an X 1 X 1 X 2 X 2 /X 1 X 2 Y multiple sex chromosome system has been reported in P. aff. motoro and P. falkneri from the upper Paraná River basin, Brazil, with 2n = 66 chromosomes for the females and 2n = 65 chromosomes for the males of both species (Cruz et al, 2011).…”

Cell culture-based shark karyotyping as a resource for chromosome-scale genome analysis

“…It is widely thought that the sex of chondrichthyans is also determined by the GSD system with XX/XY sex chromosomes 43,45 . In chondrichthyans, sex chromosomes have been reported for eight species when only those reports based on multiple individuals for both sexes are considered 15,25,[46][47][48][49] (Fig. 5, Supplementary Table 1).…”

“…Considering all existing information and our data, we conclude that chondrichthyan karyotypes are generally characterized by numerous chromosomes (up to 106), with a large distribution of chromosome lengths in a karyotype, and sometimes include heteromorphic sex chromosomes. Most chondrichthyan species remain to be analysed, but this emerging karyotypic format is distinct from that of teleost fishes with relatively constant numbers (44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54) of chromosomes that often include homomorphic sex chromosomes 13,44 . The karyotype provides information about a species' inherent chromosome number and sizes, as well as centromere positions, and provides an ultimate goal of whole-genome sequence reconstruction.…”