Karyotyping and cytogenetic mapping of Atlantic cod (Gadus morhua Linnaeus, 1758)

Abstract

Summary The Atlantic cod (Gadus morhua) is an important natural resource for northern societies and is now also considered to be a promising candidate for aquaculture. In recent years, much effort has been directed towards the development of genomic tools, and genome initiatives for Atlantic cod have been established. Despite the growing attention devoted to the Atlantic cod genomics, basic aspects of its genome structure and organization remain unknown. Thus, the present work aims to study cytogenetic features of the Atlantic cod as a contribution to the knowledge of this species' genome. The Atlantic cod displays a diploid number of 46 chromosomes, with a karyotypic formula 16 m/sm + 30 st/t. Conventional karyotyping was improved by chromosomal mapping of two classes of repetitive sequences. 18S rDNA clusters were assigned to pairs 2 and 4; small amounts of 18S rDNA clusters were occasionally detected on pair 5. These findings could not be related to the geographical origin of the specimens, but were consistent with the variability of these repeated genes in fish in general. 5S ribosomal gene clusters, apparently corresponding to a single 5S rDNA class, were detected on twelve chromosomes (pairs 11, 12, 14, 17, 20 and 21). The present update of the existing but meagre information on the karyotype of Atlantic cod, plus the first physical mapping of repetitive genes in this species herein, opens the way for an integrated approach that combines genetic and physical mapping with the assembly of the genome of this commercially important species.

Development of a continuous cell line from larval Atlantic cod (Gadus morhua) and its use in the study of the microsporidian, Loma morhua

“…The CO1 gene sequence for GML‐5 was deposited in BOLD within the project “Characterizing Cell Lines from Fish and Shellfish (CCLF)” as Process ID CCLF051‐11. Karyotype analysis (Figure b) provided a chromosome modal number of 2n = 46, in agreement with the reported karyotype modal number of 46 for G. morhua (Ghigliotti et al., ). However, only 21% of the counted spreads had the diploid karyotype characteristic of cod and aneuploid cells with 47 and 48 chromosomes accounted for a quarter of the chromosome spreads analysed.…”

Ancient chromosomal rearrangement associated with local adaptation of a postglacially colonized population of Atlantic Cod in the northwest Atlantic

“…This double inversion on LG1 is observed at higher frequencies in the migratory North East Arctic population than in coastal nonmigratory populations in the northeast Atlantic (Berg et al., ; Kirubakaran et al., ). Inversions such as this were unknown prior to the genomics era because it was difficult to produce banded karyotypes for fish species like Atlantic Cod (Ghigliotti et al., ); however due to an increase in available genomic data, we are now able to identify these inversions in Atlantic Cod and examine their role in shaping population structure across the species' range.…”

Transposable Elements in Fish Chromosomes: A Study in the Marine Cobia Species

“…Furthermore, the chromosomal mapping of repetitive DNA sequences has added complementary information on genetic linkage maps Freeman et al, 2007;Ghigliotti et al, 2012], evolution of sex chromosomes [Cioffi and Bertollo, 2012] and speciation processes in fishes [Lima-Filho et al, 2012].…”