title: Chromosomal rearrangement in pectinidae revealed by rRNA loci and implications for bivalve evolution.
abstract: Karyotype and chromosomal localization of major (18-5.8-28S) and minor (5S) ribosomal RNA genes were studied in two species of Pectinidae, zhikong (Chlamys farreri) and bay (Argopecten irradians irradians) scallops, using fluorescence in situ hybridization (FISH). C. farreri had a haploid number of 19 with a karyotype of 3m + 4sm + 7sm-st + 4st + 1st-t, and A. i. irradians had a haploid number of 16 with a karyotype of 5st + 11t. In C. farreri, the major and minor rRNA genes had one locus each and were mapped to the same chromosome-Chromosome 5. In A. i. irradians, the major rRNA genes had two loci, located on Chromosomes 4 and 8, and the 5S rRNA gene was found at a third chromosome-Chromosome 10. Results of this and other studies indicate that karyotype of A. i. irradians (n = 16, 21 arms) is secondary and derived from an ancestral karyotype similar to that of C. farreri (n = 19, 38 arms) through considerable chromosomal loss and rearrangements. The ability to tolerate significant chromosomal loss suggests that the modal karyotype of Pectinidae and possibly other bivalves with a haploid number of 19 is likely tetraploid; i.e., at least one genome duplication has occurred during the evolution of Bivalvia.
authors.affiliation: Haskin Shellfish Research Laboratory, Institute of Marine and Coastal Sciences, Rutgers University, 6959 Miller Avenue, Port Norris, New Jersey 08349, USA.
authors.forename: Yongping
authors.initials: Y
authors.lastname: Wang
authors.forename: Ximing
authors.initials: X
authors.lastname: Guo
mesh_terms: D000818:Animals; D002681:China; D002874:Chromosome Mapping; D002875:Chromosomes / Q000235:genetics*; D017931:DNA Primers; D015342:DNA Probes / Q000235:genetics; D019143:Evolution, Molecular; D020440:Gene Duplication; D015321:Gene Rearrangement / Q000235:genetics*; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D008974:Mollusca / Q000235:genetics*; D012335:RNA, Ribosomal / Q000235:genetics
chemical_list: D017931:DNA Primers; D015342:DNA Probes; D012335:RNA, Ribosomal