Wang Yongping, Guo Ximing
Haskin Shellfish Research Laboratory, Institute of Marine and Coastal Sciences, Rutgers University, 6959 Miller Avenue, Port Norris, New Jersey 08349, USA.
Biol Bull. 2004 Dec;207(3):247-56. doi: 10.2307/1543213.
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.
利用荧光原位杂交（FISH）技术，对栉孔扇贝（Chlamys farreri）和海湾扇贝（Argopecten irradians irradians）这两种扇贝科物种的主要（18 - 5.8 - 28S）和次要（5S）核糖体RNA基因的核型及染色体定位进行了研究。栉孔扇贝的单倍体数目为19，核型为3m + 4sm + 7sm - st + 4st + 1st - t，海湾扇贝的单倍体数目为16，核型为5st + 11t。在栉孔扇贝中，主要和次要rRNA基因各有一个位点，且都定位于第5号染色体。在海湾扇贝中，主要rRNA基因有两个位点，分别位于第4号和第8号染色体上，5S rRNA基因则位于第三条染色体——第10号染色体上。本研究及其他研究结果表明，海湾扇贝的核型（n = 16，21条臂）是次生的，是通过大量染色体丢失和重排，从与栉孔扇贝（n = 19，38条臂）相似的祖先核型衍生而来。耐受显著染色体丢失的能力表明，扇贝科以及可能其他单倍体数目为19的双壳类动物的模式核型可能是四倍体；也就是说，在双壳纲的进化过程中至少发生了一次基因组加倍。
