title: Chromosomal localization of rDNA genes and genomic organization of 5S rDNA in Oreochromis mossambicus, O. urolepis hornorum and their hybrid.
abstract: In this study, classical and molecular cytogenetic analyses were performed in tilapia fishes, Oreochromis mossambicus (XX/XY sex determination system), O. urolepis hornorum (WZ/ZZ sex determination system) and their hybrid by crossing O. mossambicus female x O. u. hornorum male. An identical karyotype ((2n = 44, NF (total number of chromosomal arms) = 50) was obtained from three examined tilapia samples. Genomic organization analysis of 5S rDNA revealed two different types of 5S rDNA sequences, 5S type I and 5S type II. Moreover, fluorescence in situ hybridization (FISH) with 5S rDNA probes showed six positive fluorescence signals on six chromosomes of all the analysed metaphases from the three tilapia samples. Subsequently, 45S rDNA probes were also prepared, and six positive fluorescence signals were observed on three chromosome pairs in all analysed metaphases of the three tilapia samples. The correlation between 45 rDNA localization and nucleolar organizer regions (NORs) was confirmed by silver nitrate staining in tilapia fishes. Further, different chromosomal localizations of 5S rDNA and 45S rDNA were verified by two different colour FISH probes. Briefly, the current data provide an insights for hybridization projects and breeding improvement of tilapias.
authors.affiliation: Chinese Academy of Fishery Sciences, Guangzhou 510380, People's Republic of China. mx-lu@163.com
authors.forename: Hua Ping
authors.initials: HP
authors.lastname: Zhu
authors.forename: Mai Xin
authors.initials: MX
authors.lastname: Lu
authors.forename: Feng Ying
authors.initials: FY
authors.lastname: Gao
authors.forename: Zhang Han
authors.initials: ZH
authors.lastname: Huang
authors.forename: Li Ping
authors.initials: LP
authors.lastname: Yang
authors.forename: Jian Fang
authors.initials: JF
authors.lastname: Gui
mesh_terms: D000818:Animals; D002681:China; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D004275:DNA, Ribosomal / Q000737:chemistry* / Q000235:genetics*; D005260:Female; D014644:Genetic Variation; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D008297:Male; D009697:Nucleolus Organizer Region / Q000737:chemistry; D012341:RNA, Ribosomal, 5S / Q000235:genetics*; D017210:Tilapia / Q000235:genetics*
chemical_list: D004275:DNA, Ribosomal; D012341:RNA, Ribosomal, 5S