裸体方格星虫染色体组型分析

Karyotype Analysis of Sipunculus nudus

将裸体方格星虫（Sipunculus nudus）置于0.04%秋水仙素溶液中暂养12h,取其体腔液,用盐度6.50‰的过滤海水低渗45min,1500r/min离心8min,卡诺氏液固定1h,热滴片,5%Giemsa染色,显微观察、摄影,根据Levan等的分类标准进行染色体组型分析。结果表明,裸体方格星虫的染色体基数为x=17,2n=2x=34,染色体组型为2n=2x=26m＋8sm,NF=68。除第2、3、4、8对染色体为亚中部着丝粒染色体（sm）外,其余均为中部着丝粒染色体（m）。臂比值变化范围是1.211～2.617。未发现性染色体和随体。

The samples of Sipunculus nudus were treated with 0.04% colchicine solution for 12 h. The celomic liquid was extracted, treated with 6.5%v seawater for 45 min, and then centrifuged at 1 500 r/min for 8 min. The sediment was fixed by Carnoy＇s solution. The suspension was dropped on heated slides. The slides were stained with Giemsa （5% , pH 6.8）, rinsed in distilled water and air-dried. Well-spread metaphase chromosomes were examined and photographs were taken with a photomicroseope. The chromosome types were categorized according to Levan＇s report. It was found that the basic number of chromosomes of S. nudus was x = 17, 2n = 2x = 34 and the karyotype formula was 2n = 2x = 26m ＋ 8sm, NF = 68. All chromosome pairs were metacentric, except that the chromosome pair numbers 2, 3, 4, 8 were submetacentric. Arm ratio was in range of 1.211 -2.617. No sex chromosomes and satellites were observed in the present study.