LiNbO3：Cu：Ce非挥发全息记录掺杂组份比的优化

实验研究了掺杂组份比对LiNbO3：Cu：Ce晶体非挥发全息记录性能的影响。结果表明．在全息记录过程中，掺杂组份比通过改变晶体的紫外光吸收特性而引起全息记录性能的改变。增加LiNbO3：Cu：Ce晶体中Cu和Ce的掺杂组份比会导致晶体对紫外光吸收的增强，进而提高了全息记录灵敏度和固定衍射效率。在弱氧化处理的掺有CuO和Ce2O4的质量分数分别为0.085％和0．011％的LiNbO3：Ce：Cu晶体中．得到了最高的固定衍射效率ηf=32％和记录灵敏度S=0．022cm／J。

Surface relief resonant Brewster niters with multiple channels

In this paper, a new type of resonant Brewster filters (RBF) with surface relief structure for the multiple channels is first presented by using the rigorous coupled-wave analysis and the S-matrix method. By tuning the depth of homogeneous layer which is under the surface relief structure, the multiple channels phenomenon is obtained. Long range, extremely low sidebands and multiple channels are found when the RBF with surface relief structure is illuminated with Transverse Magnetic incident polarization light near the Brewster angle calculated with the effective media theory of sub wavelength grating. Moreover, the wavelengths of RBF with surface relief structure can be easily shifted by changing the depth of homogeneous layer while its optical properties such as low sideband reflection and narrow band are not spoiled when the depth is changed. Furthermore, the variation of the grating thickness does not effectively change the resonant wavelength of RBF, but have a remarkable effect on its line width, which is very useful for designing such filters with different line widths at desired wavelength.

中国三种野生稻的遗传变异与保护生物学研究

稻属(OryzaL．)隶属禾本科(Poaceae)之稻族(OryzeaeDUmort.)，广布于全球热带与亚热带地区。目前认为该属约含20个野生种和2个栽培种，中国产4个种。亚洲栽培稻(O. sativaL．)是世界上最重要的粮食作物之一，而在中国则为第一粮食作物。在稻种基因库中，发掘野生稻中丰富的遗传多样性是解决当今人口与粮食矛盾的必由之路。因此，保护野生稻的遗传多样性举世瞩目。针对热带与亚热带地区的环境恶化而导致野生稻居群的大量绝灭与急剧萎缩的状况，制订有效的策略，最大限度地保护野生稻的遗传多样性已迫在眉睫。然而，目前对野生稻种内遗传多样性的知识十分贫乏，缺乏制订保护策略的科学基础。这一问题在中国尤为突出。本文基于1994-1995年对中国三种野生稻濒危状况的调查结果，利用等位酶分析对普通野生稻26个居群，药用野生稻8个居群和疣粒野生稻l7个居群进行了遗传多样性的研究，并重点对目前育种价值最大而濒危程度最高的普通野生稻从五个方面作了进一步的探讨。最后根据遗传多样性的研究结果讨论了它们的濒危原因，并提出了初步的保护策略。主要结果如下： 一．普通野生稻D．rufipogon Griff. 在中国的三种野生稻中，普通野生稻的遗传多样性水平最高(A=1.33，P= 0.227，Ho=0.033和He=_0.068)，遗传分化水平较低(Fst=0,310)。广西与广东的居群较其它地区的居群具有较丰富的遗传变异。因此，华南可能是中国普通野生稻的遗传多样性中心;云南现存的所有三个居群的遗传多样性水平偏低(A=1.10.p=0.148，Ho=0.007和He=0.079)，与该地区栽培稻丰富的遗传多样性形成鲜明对照，普通野生稻居群间的遗传一致度与地理距离无明显相关。 1．通过14个中央居群与5个边缘居群的对比研究表明了边缘居群的遗传结构明显不同于中央居群：其遗传多样性水平与遗传分化均低予中央居群，杂合子比中央居群更为不足。而且，从中央居群到边缘居群，位点的多态性逐渐丧失，遗传多样性水平递减，一些多态位点的等位基因频率逐渐地发生变化。 2. 通过7个受栽培稻基因渗入的居群与5个隔离较好居群的对比研究表明，被渗入居群虽然在形态上表现出复杂的变异式样，但遗传多样性水平并无相应的增高。栽培稻基因流对野生居群遗传结构的影响可能主要是遗传同化，即阻止其居群内与居群间的遗传分化。 3. 通过对2个低纬度居群与2个北缘居群两个生活史阶段的遗传多样性研究表明繁育系统是影响普通野生稻居群遗传结构的因素之一。在低纬度居群中种子阶段的遗传变异高于植株阶段，在高纬度居群中则相反。 4．通过对北缘居群(江西东乡)1980年，1985年和1994年的居群遗传结构的研究，发现该居群的遗传结构逐渐在发生变化，表现为遗传多样性水平不断下降，居群越来越偏移哈迪一温伯格平衡和杂合子变得越来越缺乏。 5．通过对一个典型的普通野生稻居群（元江居群）的居群内遗传结构的研究，表明遗传变异在3个亚居群间分布不均衡，基因型里聚集分布，使得亚居群间有一定的遗传分化。导致其居群遗传结构的亚划分的主要原因可能是有限的基因流(Nm=0.964

三种兰科植物的保护遗传学研究

本研究在野外调查的基础上，采用随机扩增多态DNA (RAPD)分析和形态学方法，研究了我国三种珍稀濒危兰科植物硬叶兜兰（Paphiopedilummicranthum）、麻栗坡兜兰（P. malipoense）和独花兰（Changnienia amoena）的遗传多样性与群体遗传结构，主要结果如下： 1．采用1 2个引物对分布于我国云贵地区的4个硬叶兜兰群体共161个体进行RAPD扩增和分析，得出物种水平的多态条带百分率（PPB）为71.6%，Nci的基因多样度(h)为0.217，Shannon多样性指数（1)为0.3301;4个群体的平均多样性水平为PPB=45.2%，h=0.1457，1= 0.2204：低于远交兰花的平均水平。分子方差分析(AMOVA)表明，在总遗传变异中，群体间遗传变异占20.31%．群体内占79.69%;POPGENE给出的基因分化系数 （Gst）为0.2958;遗传分化略高于远交物种的平均水平。空间自相关分析表明，所检测的两个群体中存在明显的空间结构，基因型在群体中以不同的小斑块存在。遗传距离和空间距离不存在相关关系。 2．用于麻栗坡兜兰的RAPD引物同上，但取样范围只有贵州的2个群体共10个个体。就所研究的个体柬看，麻栗坡兜兰的遗传多样性明显低于远交兰花物种的平均水平。物种水平上，多态条带百分率(PPB)为49.5%。Nei的基因多样度（h）为0. 1174， Shannon多样性指数(I)为0.1764：在群体水平上，上述三个指标的平均值则分别为12. 75%、0.0486和0.0712，均大大低于硬叶兜兰。然而，尽管作了种种努力，麻栗坡兜兰的取样个体数量仍很少，因此所得结果可能会有误差。 3．用16个引物对分布于河南、湖北、湖南、江西4个省11个独花兰群体共216个体进行了RA PD扩增和分析，独花兰在物种水平PPB=80. 7%，h=0.197．1=0. 3116;在群体水平，上述三个指标的平均值则分别为40. 9%、0.1247和0. 1902，均低于远交兰花的平均水平。AMOVA分析表明，11个独花兰群体间的遗传变异占43.48%，群体内的占56.52%：在神农架和新宁地区内部，群体间的遗传变异分别占13.68%和49.3g%(AMOVA)。POPGENE给出的11个群体的基因分化系数(Gst)为0.3580．神农架和新宁地区内的Gst，值分别为0.1194和0.2597。可见，群体间的遗传分化明显高于远交物种的平均水平。空间自相关分析表明，独花兰的遗传变异在群体内不存在明显的空间结构。群体之间的遗传距离和空间距离不存在相关关系。 4．对独花兰7个群体形态性状的分析发现，12个形态性状在群体内均有较高的变异性，cv值变动于0.022-0.30O。庐山群体(LS)在所有性状上的平均值均为最高。营养性状和花部性状的变异性基本一致。除花葶长和花距直径与某些花部性状之间没有显著的相关关系外，各性状之间均有显著的相关性。对XN4群体的统计没有发现假磷茎数目与其他性状之间存在显著相关性。 根据以上对硬叶兜兰、麻粟坡兜兰和独花兰遗传多样性和群体遗传结构韵研究，结合其他方面的资料;对三种兰花的濒危机制进行了初步的分析。首先，人为采挖和破坏是导致这些兰花物种濒危的直接原因，尤其是麻栗坡兜兰。其次， 适宜兰花生存的生境正在只益萎缩、退化和片段化。这两方面因素的共同作用导致上述兰花群体的数目和规模日益下降，由此引发的遗传多样性降低和遗传结构的改变进一步加剧其濒危状况。对于独花兰而言，较低的繁殖能力又使其生存状态雪上加霜。针对三个物种不同的繁殖特性和遗传学状况，提出如下保护措施。(1)硬叶兜兰由于繁殖能力较强、现存个体尚多，遗传多样性损失不甚严重，因此以保护其所在的生境为基础、实施原位保护，是比较合适的保护策略。(2)麻粟坡兜兰目前受破坏程度非常严重;所剩个体很少，遗传多样性较低，已经很难进行有效的原位保护。因此;应利用迁地保护手段抢救目前尚存的个体。(3)独花兰的繁殖能力较弱，因此在保护生境和严禁采摘的基础上，可采用人工授粉等方式，提高结实率、增加繁殖效率，促使其复壮：在进行迁地保护时，则应注意不同群体间存在较大遗传变异而群体内多样性较低这一现实。

Elasticity, band structure, and piezoelectricity of BexZn1-xO alloys

Lattice constants, elasticity, band structure and piezoelectricity of hexagonal wideband gap BexZn1-xO ternary alloys are calculatedusing firstprinciples methods. The alloys' lattice constants obey Vegard's law well. As Be concentration increases, the bulk modulus and Young's modulus of the alloys increase, whereas the piezoelectricity decreases. We predict that BexZn1-xO/GaN/substrate (x = 0.022) multilayer structure can be suitable for high-frequency surface acoustic wave device applications. Our calculated results are in good agreement with experimental data and other theoretical calculations. (c) 2008 Elsevier B.V. All rights reserved.

Structural and optical characterization of InAs nanostructures grown on high-index InP substrates

The structural and optical properties of InAs layers grown on high-index InP surfaces by molecular beam epitaxy are investigated in order to understand the self-organization of quantum dots and quantum wires on novel index surfaces. Four different InP substrate orientations have been examined, namely, (1 1 1)B, (3 1 1)A, and (3 1 1)B and (1 0 0). A rich variety of InAs nanostructures is formed on the surfaces. Quantum wire-like morphology is observed on the (1 0 0) surface, and evident island formation is found on (1 1 1)A and (3 1 1)B by atomic force microscopy. The photoluminescence spectra of InP (1 1 1)A and (3 1 1)B samples show typical QD features with PL peaks in the wavelength range 1.3-1.55 mu m with comparable efficiency. These results suggest that the high-index substrates are promising candidates for production of high-quality self-organized QD materials for device applications. (C) 1999 Elsevier Science B.V. All rights reserved.

Tellurium enhanced non-resonant third-order optical nonlinearity in a germano-silicate optical fiber

碲掺杂的高非线性石英光纤

All-optical switching application of germano-silicate optical fiber incorporated with Ag nanocrystals

银纳米晶体掺杂的高非线性石英光纤的全光转换应用

Intense green upconversion emission in Tb3+/Yb3+ co-doped alumino-germano-silicate optical fibers

Tb/Yb共掺的石英光纤的上转换绿光发光研究，研究了最佳浓度配比和发光机理。

地下结构的爆炸振动效应与冲击破坏行为研究

对爆源近区地下混凝土管道结构在爆炸冲击载荷作用下的动力学响应开展探索性实验研究。选用钢筋混凝土管道模拟地下结构，尺寸为：$\phi_{\hbox{内}}$800mm$\times$2000mm$\times$100mm。通过实验研究定量确定爆炸振动波载荷对地下结构产生的振动效应；定性确定爆炸冲击波载荷对地下管道结构和混凝土材料产生的动态破坏效应。爆炸当量分别为50 g和100 g TNT，爆炸距离取为0.1，0.3，1，7和10m。实验主要涉及地下管道结构在小药量爆炸点近区的破坏效应与爆炸药量和爆炸距离间关系的确定；混凝土材料破坏行为与药量和爆炸距离关系的确定；爆炸冲击波的影响范围以及爆炸振动波的有效影响范围与爆源特性的关系及爆炸响应函数的确定。从小当量地下结构爆炸实验观察到：地下结构的爆炸振动响应，即振动波波长和频率不同于土介质地表的波长和频率。与地表面上建筑物的波长和频率相比，振动波长持续作用时间明显缩短，且振动频率显著提高。这与地下结构的爆炸动力学响应，特别是爆源近距离的结构动力学响应存在着本质的区别。不同的爆炸距离和当量，地下爆炸对地下结构可以产生振动和冲击两种不同特征的动力学效应。在折算距离大于0.22$\sim$0.25 m/W$^{1/3}$时，100 g TNT当量的爆炸以产生振动效应为主。在折算距离小于0.22$\sim$0.25 m/W$^{1/3}$时，爆炸主要产生冲击效应；在爆炸距离小于1.5m/W$^{1/3}$时，地下爆炸振动波对结构产生的动力学响应的明显特征是管道结构发生径向变形。而且，管道上与爆源最近点是管道变形的对称点。管道的轴向和环向动力响应表现为相应方向上的刚体振动。在爆炸距离大于1.5 m/W$^{1/3}$，如等于2.15m/W1/3的情况下，爆炸振动波对管道结构产生的动力学响应主要表现为整体振动。结构的变形特征基本消失；地下爆炸冲击波载荷对爆源近区管道结构和混凝土材料可以产生三种破坏效应：在折算距离等于0.065 m/W$^{1/3}$时，低强度的冲击波载荷仅产生结构破坏效应。实验中观察到混凝土管道只沿其轴线方向上形成贯穿性裂纹，管道内外表面均无损伤和破碎现象；当折算距离等于0.027 m/W1/3时，较强冲击波载荷既引起管道的结构破坏，也产生混凝土材料的破坏。这时观察到沿混凝土管道轴线方向上，以及与轴线成30$^\circ$至50$^\circ$范围内形成贯穿性裂纹。同时在管道内表面出现直径约为210 mm的层裂区，最大层裂厚度约为8$\sim$12 mm；当折算距离等于0.022 m/W$^{1/3}$时，爆炸强冲击波载荷主要引起的混凝土材料破坏形式表现为破碎。即在管道上以爆源最近点为中心形成直径约为370 mm的贯穿性孔洞，还观察到该孔洞周边不同方向上有长度为230$\sim$410 mm不等的数条细裂纹形成。

Study of urinary 8-hydroxydeoxyguanosine as a biomarker of oxidative DNA damage in diabetic nephropathy patients

Increased oxidative stress induced by hyperglycemia may contribute to the pathogenesis of diabetic complications. Urinary 8-hydroxydeoxyguanosine (8-OHdG) has been reported to serve as a sensitive biomarker of oxidative DNA damage and also of oxidative stress. This article studied oxidative DNA damage in patients with diabetic nephropathy and in healthy control subjects by urinary 8-OHdG evaluations. Contents of 8-OHdG in urine were analyzed by capillary electrophoresis with end-column amperometric detection (CE-AD) after a single-step solid-phase extraction (SPE). Levels of urinary 8-OHdG in diabetic nephropathy patients with macroalbuminuria was significant higher than in control subjects (5.72 +/- 6.89 mumol/mol creatinine versus 2.33 +/- 2.83 mumol/mol creatinine, P = 0.018). A significant difference of 24 h urinary 8-OHdG excretions exists between the patients with macroalbuminuria and the patients with nonnoalbuminuria (19.2 +/- 16.8 mug/24 h versus 8.1 +/- 1.7 mug/24 h, P = 0.015). There was a positive correlation between urinary excretion of 8-OHdG and glycosylated hemoglobin (HbA(1)c) (r = 0.287, P = 0.022). A weak correlation exists between the levels of 8-OHdG and triglyceride (r = 0.230, P = 0.074). However, the urinary 8-OHdG contents are not correlated with blood pressure and total cholesterol. The increased excretion of urinary 8-OHdG is seen as indicating an increased systemic level of oxidative DNA damage in diabetic nephropathy patients. (C) 2004 Elsevier B.V. All rights reserved.

Study on QSPR of alcohols with a novel edge connectivity index F-m

A novel edge degree f(i) for heteroatom and multiple bonds in molecular graph is derived on the basis of the edge degree delta(e(r)). A novel edge connectivity index F-m is introduced. The multiple linear regression by using the edge connectivity index F-m and alcohol-type parameter delta, alcohol-distance parameter L can provide high-quality QSPR models for the normal boiling points (BPs), molar volumes (MVs), molar refraction (MRs), water solubility(log(1/S)) and octanol/water partition (logP) of alcohols with up to 17 non-hydrogen atoms. The results imply that these physical properties may be expressed as a liner combination of the edge connectivity index and alcohol-type parameter, 6, alcohol-distance parameter, L. For the models of the five properties, the correlation coefficient r and the standard errors are 0.9969,3.022; 0.9993, 1.504; 0.9992, 0.446; 0.9924,0.129 and 0.9973,0.123 for BPs, MVs, MRs, log(1/S) and logP, respectively. The cross-validation by using the leave-one-out method demonstrates the models to be highly reliable from the point of view of statistics.

Electrochemical reactions of cyanocobalamin in acidic media

Electrochemical reactions of cyanocobalamin, CN-Cbl[Co(III)], were studied at glassy carbon electrodes in acidic media by means of cyclic voltammetry and differential pulse polarography. It was found that in pH 0 solution, CN-Cbl[Co(III)] exists mainly in the base-off form, {CN-Cbl[Co(III)]}(base-off). It can undergo a one-electron reduction and a follow-up chemical reaction to form {H2O-Cbl[Co(II)]}(base-off). The rate-constant k of the follow-up decyanation reaction is 0.022 s(-1). {H2O-Cbl[Co(II)]}(base-off) is further reduced to obtain H2O-Cbl[Co(I)]. (C) 1997 Elsevier Science S.A.

栉孔扇贝抗鳗弧菌感染性状候选基因的多态性研究

栉孔扇贝（Chlamys farreri）是我国北方地区主要的养殖贝类之一，曾为沿海各省带来巨大的经济效益。但自1997年以来，陆续爆发的病害问题给扇贝养殖业造成了巨大的经济损失，严重影响了该产业的健康发展。目前认为培育抗病性强的扇贝优良品种是解决病害问题的根本途径。由于传统的育种方法费时费力，无法满足对良种的迫切需求，因此有必要通过分子手段加快抗病品种的培育步伐。标记辅助育种（marker assisted selection，MAS）是成功应用于动物育种中的分子手段之一，但由于缺乏与抗病性状相关的标记，MAS目前还无法在软体动物中得到应用。因此，寻找与抗病性状相关的分子标记是在软体动物中发展MAS的关键。 本研究利用鳗弧菌（Listonella anguillarum）对栉孔扇贝进行攻毒感染实验，初步得到敏感群体和抗病群体后采用PCR、PCR-RFLP、Bi-PASA PCR等方法研究了CfLysG、CfC1qDC和CfLITAF基因多态性及其与栉孔扇贝对鳗弧菌抗性的关系。 研究发现，栉孔扇贝CfLysG的基因序列中共有104个单核苷酸多态性（SNP）位点和29个插入/缺失（I/D）多态性位点。有17个多态性位点位于启动子区域，选择其中的-753 I/D、-391A/G和-284I/D多态性进行检测，发现这三个位点的基因型在敏感群体和抗病群体中的分布均符合Hardy-Weinberg平衡（P>0.05）。其中-753 ID基因型和-284 ID基因在抗病群体中的频率高于在敏感群体中的频率，但两者之间无显著性差异（P>0.05）。-391 AG基因型在抗病群体中的频率显著高于敏感群体（P=0.007），表明-391 AG基因型与栉孔扇贝对鳗弧菌的抗性显著相关。为验证这一相关性，对-391位点不同基因型的扇贝进行攻毒感染实验。统计发现，具有-391 AA基因型的扇贝累计死亡率显著高于具有-391 AG基因型的扇贝（P=0.001），进一步证实了CfLysG基因-391 AG基因型与栉孔扇贝对鳗弧菌的抗性显著相关。CfLysG基因的外显子共有3处SNP，其中仅第三外显子上的+3473 A/C为非同义突变。统计分析表明，+3473位点不同基因型在敏感群体中的分布频率符合Hardy-Weinberg平衡（P>0.05），而在抗病群体中则偏离Hardy-Weinberg平衡（P<0.01）。+3473 AA基因型在抗病群体中的频率显著高于在敏感群体中的频率（P=0.022），表明+3473 AA基因型与栉孔扇贝对鳗弧菌的抗性显著相关。CfLysG基因第1内含子存在+96 I/D和+487 I/D两处大片段的I/D多态性。统计发现，这两个位点的基因型在敏感群体和抗病群体中的分布频率均符合Hardy-Weinberg 平衡（P>0.05）。其中+96 DD基因型和+487 ID基因型在抗病群体中的频率均略高于在敏感群体中的频率，但两者之间无显著性差异（P>0.05）。表明这两个位点的多态性与栉孔扇贝对鳗弧菌的抗性无显著相关性。对CfLysG基因各多态性位点的统计分析表明，各位点之间存在不同程度的连锁不平衡，提示有单体型的存在。对19种频率>1%的单体型在敏感群体及抗病群体中的频率进行分析，发现-753 I/-391 G/-284 I/+96 I/+487 D/+3473 A单体型在抗病群体中的频率显著高于敏感群体（P=0.044），表明该单体型与栉孔扇贝对鳗弧菌的抗性显著相关。 在栉孔扇贝CfC1qDC基因cDNA序列上共发现14处SNP。对+423 T/C多态性与栉孔扇贝对鳗弧菌抗性的关系进行了分析。统计发现，+423位点各基因型在敏感群体和抗病群体中的分布均符合Hardy-Weinberg平衡（P>0.05）。+423 TT基因型在抗病群体中的频率显著高于在敏感群体中的频率（P=0.005），表明+423 TT基因型与栉孔扇贝对鳗弧菌的抗性显著相关。 在栉孔扇贝CfLITAF基因cDNA序列中共发现3处SNP及1处I/D多态性。对+145 I/D多态性进行研究，发现所有敏感个体及抗病个体中均同时存在+145 位点所有等位基因，表明+145位点多态性与栉孔扇贝对鳗弧菌的抗性不相关。 以上研究表明，栉孔扇贝CfLysG基因-391 AG基因型、+3473 AA基因型、-753 I/-391 G/-284 I/+96 I/+487 D/+3473 A单体型以及CfC1qDC基因+423 TT基因型与栉孔扇贝对鳗弧菌的抗性显著相关，提示它们可作为与栉孔扇贝抗病相关的候选分子标记应用于贝类抗病育种中，为贝类的标记辅助育种提供参考。此外，抗病相关分子标记的发现还有利于加深对扇贝发病机理的理解，并有助于发掘预防及治疗贝类疾病的新方法。

Different responses to selection in two stocks of the bay scallop, Argopecten irradians irradians Lamarck (1819)

Two different stocks (A and B) of the bay scallop Argopecten irradialls irradians (Lamarck, 1819) were used to test mass selection on growth. Stock A was a descending stock from the initial introduction from U.S.A. in 1982, which had been cultured in China for about 20 years. Stock B was the third generation from a recent introduction from U.S.A. in 1999. Truncation selection was conducted by selecting the largest 11% scallops in shell length from Stock A and the largest 12.7% scallops from Stock B as parents for the respective selected groups. Before the removal of parents for truncation selection, equal numbers of scallops were randomly chosen from Stock A and B to serve as parents for the control groups. Offspring from the four groups were reared under the same hatchery, nursery, and grow-out conditions. Values of response to selection and realized heritability at larvae, spat and grow-out stages for Stock B were all significantly (P < 0.001) higher than its counterpart for Stock A. For Stock A, no significant response to selection was observed (P > 0.05) at any stage, and the realized heritability for shell length was 0.015 +/- 0.024 for larvae, 0.040 +/- 0.027 for spat, and 0.080 +/- 0.009 for grow-out, respectively. For Stock B, however, significant (P < 0.05) response to selection was observed, and the realized heritability for shell length was 0.511 +/- 0.010 for larvae, 0.341 +/- 0.022 for spat, and 0.338 +/- 0.015 for grow-out. On average, responses to selection at the three stages for Stock B was 30 x, 7.1 x, and 3 x higher than its counterpart for Stock A, respectively. Accordingly, realized heritability at above stages for Stock B was 33 X, 7.5 x, and 3.2 X higher than its counterpart for Stock A, respectively. Differences in response to selection and realized heritability between the two stocks are presumably due to differences in genetic variability. As the 20th generation from the initial introduction consisted of only 26 scallops, Stock A is known to be highly inbred, while inbreeding in Stock B is negligible. (C) 2004 Elsevier B.V. All rights reserved.