The spotted knifejaw, Oplegnathus punctatus, is an important aquaculture fish species in China. To better understand the chromosomal microstructure and the karyotypic origin of this species, cytogenetic analysis was performed using Giemsa staining to identify metaphase chromosomes, C-banding to detect C-positive heterochromatin, silver staining to identify the nucleolus organizer regions (Ag-NORs), and fluorescence in situ hybridization (FISH) for physical mapping of the major (18S rDNA) and minor (5S rDNA) ribosomal genes. The species showed a karyotype of 2n = 48 for females, composed of 2 submetacentric and 46 telocentric chromosomes, with a fundamental number (FN) = 50, while the karyotype of males was 2n = 47, composed of 1 exclusive large metacentric, 2 submetacentric, and 44 telocentric chromosomes, with FN = 50. These karyotype results suggest that O. punctatus might have an XXXX/XXY multiple sex chromosome system. C-positive heterochromatin was distributed in the centromeres of all chromosomal pairs and in the terminal portions of some chromosomes. A single pair of Ag-positive NORs was found to be localized at the terminal regions of the short arms of the subtelocentric chromosome pair, which was supported by FISH of 18S rDNA. After FISH, 5S rDNA were located on the interstitial regions of the smallest telocentric chromosome pair. This study was the first to identify the karyotype of this species and will facilitate further research on karyotype evolution in the order Perciformes.

ABSTRACT. Bone morphological protein7 (BMP7), a member of the transforming growth factor-β (TGF-β) family, was first identified because of its ability to induce ectopic chondro-osteogenesis in vivo. It also plays a crucial role in the growth, development, and physiological functioning of the reproductive system. Among intraovarian growth factors, many studies have shown that BMP7 plays a pivotal role in regulating the early phases of follicular growth. We detected a 5-bp insertion-deletion at 602 bp upstream from the transcription start site of the BMP7 gene promoter among 258 pigs of 3 breeds. Along with 2 homoduplex DNAs, another 4 previously unknown bands (named A, B, C, and D) were detected by non-denaturing polyacrylamide gel electrophoresis. By DNA sequencing, we found that PCR products from heterozygotes contained 2 homoduplexes and 4 heteroduplexes. Genetic polymorphism analysis revealed 3 genotypes (AA, AB, and BB) at this site; the distribution of these genotypes followed HardyWeinberg equilibrium. A was the dominant allele (0.715), and AA was the dominant genotype (0.500). The polymorphism information Porcine BMP7 gene promoter indel content value was calculated to be 0.325, the expected heterozygosity was 0.407, and effective number of alleles was 1.688, indicating an intermediate degree of polymorphism and good potential for selection and breeding. Highly significant differences were found between different breeds and distributions of genotypes. Based on correlation analysis, the 5-bp indel site does not significantly affect porcine reproductive traits (total number of births, number of piglets born alive, litter birth weight, and litter weight at 21 days; P > 0.05), which was consistent with the results of genetic variation analysis.