| 摘要: |
| 于1994年8月在山东省威海和青岛市沿海采集缢蛏，运用PHA（每克体重8×10-6 g）和秋水仙素（每克体重2–3×10-6 g）体内注射法，以其鳃组织为材料，对缢蛏的染色体进行分析研究。结果表明，缢蛏的二倍体数目为2n＝38，核型为26m＋8sm＋2st＋2t，NF＝72。C-带核型展示，有7对染色体恒定地出现C-带，均为端带。银染核型表明，有一对中着丝粒染色体具Ag－NOR带。银染带可以作为一种遗传标记。 |
| 关键词: 核型 C-带 银染带 缢蛏 |
| DOI： |
| 分类号: |
| 基金项目:国家攀登计划B项目!PD－B6－5－1号 |
附件 |
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| CHROMOSOME STUDY OF SINONOVACULA CONSTRICTA (BIVALVIA) |
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WANG Jin-xing,ZHAO Xiao-fan,ZHOU Ling-hua,XIANG Jian-hai
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1.College of Life Sciences, Shandong University, Jinan, 250100;2.Insititule of Oceanology, The Chinese Academy of deiences, Qingdao, 266071
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| Abstract: |
| Individuals of Sinonovacula constricra were collected from the coastal areas of Weihai and Qingdao, Shandong Province. The animals were injected in vivo with 8 μg of phytohemagglutinin (PHA) per gram of body weight including shell weight. After being cultured for 18 to 24 hours, Colchicine was injected (2 to 3 μg per body weight). Four to five hours later, the gills were taken out and sectioned into pieces. The gill cells were treated with hypotonic solution (0.075 mol/L KCI) for around 40 minutes at room temperature, and fixed in fresh methanol: acetic acid (3:1) three times. Metaphase chromosome spreads were prepared using the conventional air-dry method. The diploid chromosome number was determined by observing 100 metaphase plates; of those ten well-spread plates were photographed with an Olympus microscope. Classification of chromosomes was based upon the study of Levan et al (1964).
The method for the staining of constitutive heterochromatin was according to Sumner (1972) with slight modifications. Slides were treated for 30 minutes in 0.2 mol/L HCl at room temperature and incubated in 5% Ba(OH)2, for 30 to 60 seconds at 37oC. After washing with distilled water, slides were subsequently incubated in 2×SSC solution for 2 hours at 60oC. Staining was done in 5% Giemsa (pH= 7.0) for 10 minutes. Silver-staining was performed according to Howell et al (1980). The results are as follow.
The distribution of chromosome counts obtained for S. constricta is shown in Tab. 1. The measurements and classification of the ten selected metaphase plates were presented in Tab.2. Plate I shows the karyotype arranged by morphology and decreasing chromosome size. The diploid chromosome number is 38. All chromosomes were matched in l9 pairs; they were divided into 3 groups. Group A includes pairs 1 to 13 that are metacentrics. The relative lengths of pairs 1 to 3 are larger than the others; thus, they can be identified easily. The relative lengths of the others decrease gradually. Group B consists of pairs 14 to 17 which are submetacentrics. Pair 14 is larger than the others. The relative lengths of the others decrease gradually and they cannot be distinguished easily from each other. Group C includes chromosome No.18 and 19. No.18 is subtelocentric and No.19 telocentric. They can be identified easily in all chromosomes of S. constricta.
Therefore, the karyotype of S. constricta is 2n = 38, 26m+ 8sm+ 2st+ 2t, NF= 72 (Plate II: 1, 2).
The C-banded chromosomes of S. constricta reveal constitutive heterochromatin in the telomeric region of 7 pairs of the chromosomes. Among them, 6 pairs (No.1, 5, 9, 10, 11, and 13) are metacentrics and 1 pair (No.16) is submetacentric. In addition, Pairs 4 and 14 show interstitial C-bands and chromosome. No.18 has telomeric C-band occasionally. No centromeric C-band was found in the karyotype of S. constricta (Plate I: 3, 4).
Nine silver-stained metaphases of S. constricta were analyzed. A variable number of Ag-NORs was detected, which varied between 0 and 2 chromosomes in different metaphases of the species. The silver-stained karyotype of the species shows one chromosomal pair (metacentric) with telomeric NORs. The variation of NORs observed in the metaphase chromosomes is also expressed in interphase nuclei (Plate I: 5 to 8).
In conclusion, the employment of PHA injection in the investigation of chromosomes in S. constricta can increase the index of mitosis in gill cells. The heterochromatin is located in the telomeric regions of seven pairs of chromosomes. The silver-stained bands are constantly located at one pair of metacentric chromosomes. Thus, the Ag-NORs can be regarded as chromosome markers of this species in the genetic breeding and other fields of studies. |
| Key words: Karyotype, C-banding, Ag-NORs, Sinonovacula constricta |
