Abstract
To provide markers to identify chromosomes in the genome of octopods, chromosomes of three octopus species were subjected to NOR/C-banding. In addition, we examined their genome size (C value) to submit it to the Animal Genome Size Database. Silver staining revealed that the number of Ag-nucleoli was 2 (Octopusminor (Sasaki, 1920)), 2 (Amphioctopusfangsiao (d’Orbigny, 1839)) and 1 (Cistopuschinensis Zheng et al., 2012), respectively, and the number of Ag-nucleoli visible was the same as that of Ag-NORs on metaphase plates in the same species. In all analyzed metaphases, Ag-NORs were mainly located terminally on the long arms of chromosomes 3 (3rd) of O.minor and on the short arms of chromosomes 4 (4th) of A.fangsiao, whereas only one of the chromosomes 23 (23rd) was found Ag-NORs of C.chinensis. C-bands were localized predominantly in the centromeric regions of chromosomes in the three species, while other conspicuous stable C-bands were observed in terminal regions, including the Ag-NORs. That means these three chromosome pairs (3rd, 4th and 23rd) could be considered species-specific cytogenetic markers. The mean C values of O.minor, A.fangsiao and C.chinensis were 7.81±0.39 pg (0.070 pg per unit length), 8.31±0.18 pg (0.068 pg per unit length) and 5.29±0.10 pg (0.038 pg per unit length), respectively, and results showed that C values of the three species were not proportional to the relative length of the chromosomes. These cytogenetic characteristics will provide more theoretical foundation for further researches on chromosome evolution in octopods.
Highlights
Genetics and cytology combine to establish cytogenetics, mainly from the perspective of cytology, especially from a chromosome structure and function as well as the relationship between chromosomes and other organelles, to elucidate the mechanism of inheritance and variation
Twenty-four metaphases were counted indicating there were 2 Ag-nucleolus organizer region (NOR), 7 of them were selected for karyotype analysis and Ag-NOR loci were located on the long arms of metacentric chromosomes 3 (3rd)
Eighteen metaphases were counted and 7 of them were selected for karyotype analysis, showing there were 2 Ag-NORs and Ag-NOR loci were located on the short arms of the metacentric chromosomes 4 (4th)
Summary
Genetics and cytology combine to establish cytogenetics, mainly from the perspective of cytology, especially from a chromosome structure and function as well as the relationship between chromosomes and other organelles, to elucidate the mechanism of inheritance and variation. Previous published reviews on chromosomal studies of molluscs were greatly increased since cytogenetic techniques including silver-staining, C-and G-banding and have begun to be applied to molluscan chromosomes (Thiriot-Quiévreux 2003). These techniques have been widely used in the study of shellfish chromosomes, there are no reports on the cephalopods. Due to the restriction of the embryo acquisition, and the number of cephalopod chromosomes up to 60, it is difficult to obtain an ideal metaphase All these factors seriously restrict the cytological study of cephalopods. The present study used gills as materials, and through a large number of repeated tests, the ideal metaphases with NORs and C-bands were obtained based on the previous study
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