一种以准DOG分布为基元的体视匹配算法

本文提出了一种新体视的匹配算法,其特点是:(1)以准DOG分布为基元;(2)以同源性、唯一性、顺序性为约束;(3)本质上是一种协同算法。理论分析和实际计算表明,该算法是合理的,有效的。最近的一些心理物理学结果是支持我们的这个算法的。     

青海省阿尼玛卿山地区植物区系研究

阿尼玛卿山地区位于青海省东南部,约占北纬33°25′～36°20′,东经98°50′～102°25′。本地区共有种子植物56科、251属、752种。区系特征如下:(1)种类相对较少,特有属相对较多;(2)以北温带为主的温带性质明显;(3)在种一级水平上,以中亚成分和东亚成分,特别是其中各自联系着喜马拉雅的变型成分为主的分布,形成了区内以欧亚大陆温、寒地带典型成分为优势的、明显的温带性质及其高原、高山分布的特点;(4)植物的生活型以多年生草本为主,木本种较少,乔木更少;(5)在中国特有种的分析中,本区系与横断山和甘肃南部区系的联系最为密切;(6)生态环境对本区系特征的塑造表现为高寒生态因子的选择和高山特化的作用强烈,而在一定程度上湿冷生性质和寒旱生性质的高山特化作用更为明显;(7)表现出青藏高原植物区系的衍生性和年轻性;(8)植被以由嵩草属植物为建群种的高寒草甸和由金露梅、山生柳等分别为建群种的高寒灌丛为主;(9)以绿绒蒿等所体现的地区特色明显。综上所述,本区同唐古特地区在区系性质和特点等方面基本一致,所以,本地区不仅是唐古特地区植物区系中的一个具有代表性的区系之一,而且是其核心区系之一。     

基于SolVES模型的生态系统文化服务价值评估——以浙江省武义县南部生态公园为例

文化服务是一种重要的生态系统服务类型,也是连接生态系统和社会系统的重要桥梁。以浙江省武义县南部生态公园为研究对象,以规划应用为导向,以Sol VES模型为基础,以专家调查法为补充,以价值指数(VI)评估生态系统文化服务价值,结果表明:(1)武义县南部生态公园中部及北部生态系统文化服务价值较高,东北部存在一条价值较高的生态系统文化服务带;(2)牛头山、延福寺、柳城畲族镇—十里荷花等是生态系统文化服务价值较高的热点地区;(3)受访专家认为美学、文化遗产、康养、消遣娱乐价值较为重要,教育、宗教与精神价值重要程度相对较低;(4)6种生态系统文化服务价值均与距道路、水体距离呈负相关关系,林地对应的VI范围最广,农田、水域对应的VI相对较高。将评估结果应用于武义县南部生态公园总体规划,为其提出空间布局与环境要素改善等方面的建议。通过本研究发现,SolVES模型与专家调查法相结合是一种适用于规划应用的文化服务价值评估方法,可为管理决策提供知识和技术支持。     

湖南安息香属植物的叶片比较解剖学研究

利用光学显微镜和扫描电镜对湖南产安息香属10种植物叶表皮微形态和解剖结构进行了观察和测量。结果表明:(1)表皮均由单层细胞构成,细胞形状为多边形和无规则形,垂周壁式样为平直、弓形、波状;(2)气孔器大小及密度在种间的差异明显;(3)气孔外拱盖内缘主要为波状和浅波状,气孔器外围角质纹饰以越南安息香的鸟巢状和栓叶安息香的碗状为显著区别特征;(4)老鸹铃、垂珠花和白花龙的气孔器保卫细胞两极有"T"形加厚;(5)栓叶安息香和大果安息香叶上表皮由大型细胞组成;(6)叶肉分化为栅栏组织和海绵组织,二者的厚度及比值在种间有明显的差异,其中越南安息香栅栏组织分化为2层;(7)大果安息香和芬芳安息香的主脉维管组织构成一圈封闭的环状结构,而其他种则为开放的半圆形结构;(8)叶片及主脉的厚度在种间差异明显。安息香属植物的表皮微形态及解剖结构特征比较稳定,可作为种间鉴定和分类的重要依据。     

超声诱导基因转移

植物基因工程的关键技术之一,是把外源基因导入植物细胞.目前,植物细胞的基因转移方法有:(1)农杆菌Ti或Ri质粒载体法;(2)病毒载体法;(3)磷酸钙核酸沉淀吸收法;(4)PEG介导DNA直接转移法;(5)脂质体载体法;(6)显微注射法;(7)电激基团转移法:(8)基因枪喷射法;(9)激光微束法等.前两种方法是以生物体作为载体介导基因转移,属生物方法中间三种方法是以化学药物介导基因转移.属化学方法;后四种是以物理手段介导基因转(?)属物理方法.由于物理方法操作比较简单,不受宿主范围的限,因此近年(?)发展迅速.     

一种优良淡水鱼——团头鲂（Megalobrama amblycephala）的繁殖和饲养

团头鲂原是一种野生的草食性淡水鱼类,从1960年起对它进行了一系列的观察试验,肯定它有以下六个优点：(1)在池养条件下,性腺能发育成熟;(2)以各种草类为主要食料;(3)抗病力强、成活率高;(4)容易捕捞、起水率高;(5)含肉量高,脂多、味美;(6)一年半可长至商品规格。试验结果证明团头鲂可以作为新的养殖对象,同时也提供了一套繁殖、饲养管理方法。1964年到1973年已有二十一个省市先后进行移殖饲养,有的已就地繁殖、推广。本文系历年试验和部分移殖经验的总结。     

论中国软骨鱼类的地理分布和区系特征

中国的软骨鱼类,就现时所知,共有127种、60属、28科,可归纳为如下14大类:(1)六鳃鲨类,有六鳃鲨1科3属3种;(2)虎鲨类,有虎鲨1科1属2种;(3)鼠鲨类,有锥齿鲨、鼠鲨、姥鲨、长尾鲨、须鲨和鲸鲨6科11属18种;(4)猫鲨类,有猫鲨、皱唇鲨、真鲨和双髻鲨4科19属43种;(5)角鲨类,只有角鲨1科2属4种;(6)锯鲨类,有锯鲨1科1属1种;(7)扁鲨类,有扁鲨1科1属2种;(8)锯鳐类,有锯鳐1科1属2种;(9)犁头鳐类,有犁头鳐和团扇鳐2科4属9种;(10)电鳐类,有电鳐和单鳍电鳐2科3属5种;(11)真鳐类,只真鳐1科1属7种;(12)魟类,有魟和燕魟2科5属17种;(13)鲼类,有鲼、鹞鲼、牛鼻鲼和蝠鲼4科6属12种;(14)银鲛类,只有银鲛1科2属2种。中国软骨鱼类的区系组成的特点以真鲨科、魟科和鲼科最为繁盛,其次是须鲨、猫鲨、长尾鲨和双髻鲨等科,但角鲨科、真鳐科和银鲛科的代表性则均较弱。中国软骨鱼类可分为暖水性种、暖温性种和冷温性种三种类型。暖水性种有74种,占中国软骨鱼类总数的59%;暖温性种有39种,占30%;冷温性种有14种,占11%。     

应重视生物课本中插图的使用

(一) 生物课本中的插图是教学内容的重要组成部分生物教材中的各类插图、画页,是教学内容不可分割的组成部分。以高中《生物》课本为例,在全书206页中,就有插图84幅,占全书篇幅的九分之一左右。这些插图大致可以分为六种类型:(1)形态结构图25幅,其中包括生物结构示意图和生物模式图;(2)发生发展过程图14幅,包括反映细胞分裂过程、生物个体发育过程、生物进化过程的插图等;(3)实验图17幅,主要是遗传实验的图解;(4)比较图9幅,包括核质遗传比较图、生物的进化比较图等;(5)生态图8幅,包括反映生物种间关系图和生物与环境关系图等;(6)其他图、表10幅。课文中     

一种优良淡水鱼——团头鲂(Megalobrama amblycephala)的繁殖和饲养

团头鲂原是一种野生的草食性淡水鱼类,从1960年起对它进行了一系列的观察试验,肯定它有以下六个优点:(1)在池养条件下,性腺能发育成熟;(2)以各种草类为主要食料;(3)抗病力强、成活率高;(4)容易捕捞、起水率高;(5)含肉量高,脂多、味美;(6)一年半可长至商品规格。试验结果证明团头鲂可以作为新的养殖对象,同时也提供了一套繁殖、饲养管理方法。1964年到1973年已有二十一个省市先后进行移殖饲养,有的已就地繁殖、推广。本文系历年试验和部分移殖经验的总结。       

锦鸡儿属植物区系成份分析

锦鸡儿属(Caragana Fabr.)属蝶形花科山羊豆族,是温带亚洲的代表属之一。本文对锦鸡儿属已知种类的区系成份进行了研究,将105种植物共划分为20个分布区类型,其中包括:(1)青藏高原分布;(2)沿喜马拉雅分布;(3)云贵高原分布;(4)云贵高原—华北分布;(5)秦岭山地分布;(6)华北分布;(7)中国东北分布;(8)蒙古高原分布;(9)西伯利亚阿尔泰分布;(10)亚洲中部分布;(11)西亚分布;(12)天山山地分布;(13)帕米尔—阿赖依分布;(14)小亚细亚—里海—哈萨克斯坦分布;(15)准噶尔—哈萨克斯坦分布;16)塔尔巴哈台—准噶尔—蒙古分布;(17)准噶尔特有分布;(18)昆仑山特有分布;(19)黑海—西西伯利亚分布;(20)欧洲—高加索分布。统计结果表明:属青藏高原分布的种类最为丰富,有18种,占总数的17.16％,沿喜马拉雅分布次之,共计12种,占总数的11.45％;再次之是中国华北分布和天山山地分布,均为10种,占总数的9.54％。通过区系分析可以清晰地看出:本属在中国,的分布很广,种类也很多,共计80种,约占全属总数的76.32％。中国特有种也很丰富,共计43种,占全国分布总数的一半以上(53.75％),占本属总数的40.95％。     

A computer algorithm for representing spatial-temporal structure of human motion and a motion generalization method

Inspired by the generalized motor program (GMP) theory, this study presents a symbolic motion structure representation (SMSR) algorithm that identifies a basic spatial-temporal structure of a human motion. The algorithm resolves each joint angle-time trajectory of a multi-joint motion into a sequence of elemental motion segments and labels each motion segment with a symbol representing its shape ("U": monotonically increasing; "D": monotonically decreasing; "S": stationary). By concatenating symbols according to their order in time, the spatial-temporal structure of a joint angle-time trajectory is represented as a symbolic string. The structure of a multi-joint motion is then represented as a set of symbolic strings. A sample motion, whose structure is identified by the SMSR algorithm, can be generalized to produce an infinite number of similar motion variants. To generate a variant of a sample motion, segment boundary points of the sample motion are first relocated to new locations in the angle-time space, and then individual motion segments of the original joint angle trajectories are shifted and proportionally rescaled to fit the new segment boundary points. This motion generalization method provides a basis for developing GMP-based motion simulation models, and exploring ideas and hypotheses related to the GMP theory through simulation. As an application of the motion generalization method, a motion modification (MoM) algorithm is presented, which adapts existing reach motions for new target locations. Some examples generated by the MoM algorithm are illustrated.     

Translocation within the acceptor helix of a major tRNA identity determinant

The genetic code is defined by the specific aminoacylations of tRNAs by aminoacyl-tRNA synthetases. Although the synthetases are widely conserved through evolution, aminoacylation of a given tRNA is often system specific-a synthetase from one source will not acylate its cognate tRNA from another. This system specificity is due commonly to variations in the sequence of a critical tRNA identity element. In bacteria and the cytoplasm of eukaryotes, an acceptor stem G3:U70 base pair marks a tRNA for aminoacylation with alanine. In contrast, Drosophila melanogaster (Dm) mitochondrial (mt) tRNA(Ala) has a G2:U71 but not a G3:U70 pair. Here we show that this translocated G:U and the adjacent G3:C70 are major determinants for recognition by Dm mt alanyl-tRNA synthetase (AlaRS). Additionally, G:U at the 3:70 position serves as an anti-determinant for Dm mt AlaRS. Consequently, the mitochondrial enzyme cannot charge cytoplasmic tRNA(Ala). All insect mitochondrial AlaRSs appear to have split apart recognition of mitochondrial from cytoplasmic tRNA(Ala) by translocation of G:U. This split may be essential for preventing introduction of ambiguous states into the genetic code.     

FRET multiphoton spectral imaging microscopy of 7-ketocholesterol and Nile Red in U937 monocytic cells loaded with 7-ketocholesterol

OBJECTIVE: To show the effect of 7-ketocholesterol (7KC) on cellular lipid content by means of flow cytometry and the interaction of 7KC with Nile Red (NR) via ultraviolet fluorescence resonance energy transfer (FRET) excitation of NR on U937 monocytic cells by means of 2-photon excitation confocal laser scanning microscopy (CLSM). STUDY DESIGN: Untreated and 7KC-treated U937 cells were stained with NR and analyzed by flow cytometry and CLSM. 3D sequences of images were obtained by spectral analysis in a 2-photon excitation CLSM and analyzed by the factor analysis of medical image sequences (FAMIS) algorithm, which provides factor curves and images. Factor images are the result of the FAMIS image processing method, which handles emission spectra. In FRET analysis, preparations are screened at selected UV wavelengths to avoid emission of NR in the absence of 7KC. RESULTS: During 7KC-induced cell death,flow cytometry and CLSM revealed a modification of the cellular lipid content. Factor images show FRET occurrence and subsequent colocalization of 7KC and NR. CONCLUSION: This investigation established the utility of 2-photon excitation CLSM to assess colocalization of 7KC with NR by FRET and to identify and distinguish polar and neutral lipids stained by NR that accumulate from the effect of 7KC.     

Analysis of donor splice sites in different eukaryotic organisms

We present here a new algorithm for functional site analysis. It is based on four main assumptions: each variation of nucleotide composition makes a different contribution to the overall binding free energy of interaction between a functional site and another molecule; nonfunctioning site-like regions (pseudosites) are absent or rare in genomes; there may be errors in the sample of sites; and nucleotides of different site positions are considered to be mutually dependent. In this algorithm, the site set is divided into subsets, each described by a certain consensus. Donor splice sites of the human protein-coding genes were analyzed. Comparing the results with other methods of donor splice site prediction has demonstrated a more accurate prediction of consensus sequences AG/GU(A,G), G/GUnAG, /GU(A,G)AG, /GU(A,G)nGU, and G/GUA than is achieved by weight matrix and consensus (A,C)AG/GU(A,G)AGU with mismatches. The probability of the first type error, E1, for the obtained consensus set was about 0.05, and the probability of the second type error, E2, was 0.15. The analysis demonstrated that accuracy of the functional site prediction could be improved if one takes into account correlations between the site positions. The accuracy of prediction by using human consensus sequences was tested on sequences from different organisms. Some differences in consensus sequences for the plant Arabidopsis sp., the invertebrate Caenorhabditis sp., and the fungus Aspergillus sp. were revealed. For the yeast Saccharomyces sp. only one conservative consensus, /GUA(U,A,C)G(U,A,C), was revealed (E1 = 0.03, E2 = 0.03). Yeast is a very interesting model to use for analysis of molecular mechanisms of splicing. Received: 14 October 1996 / Accepted: 30 January 1997     

A revision of the western Palaearctic species of Urophora Robineau-Desvoidy (Diptera: Tephritidae)

Abstract A key is provided to twenty-four western Palaearctic species of Urophora Robineau-Desvoidy. The hosts of twenty-three species which attack Asteraceae are listed, including those being used or investigated as possible weed biocontrol agents. The species are divided into four species groups and the differing host relationships and types of galls induced by these groups are discussed. U.lopholomae sp.n. and U.affinis ssp. calcitrapae ssp.n., associated with Centaurea (Lopholoma) spp. and C. (Calcitrapa) spp. respectively, are described. U. algerica (Hering) and U.sjumorum (Rohdendorf) are both treated as subspecies of U. quadrifasciata (Meigen). U.pontica is given full specific status and U.hispanica is removed from synonymy. The following new synonymies are made (junior synonyms in parentheses): U. angustifascia (Hering) (= Euribia phaeocera Hering); U. cardui (Linnaeus) (= U. reaumurii Robineau-Desvoidy, lectotype designated); U. jaceana (Hering) (= E.conyzae Hering); U.maura (Frauenfeld) (= E. tecta Hering); U. mauritanica Macquart (= U. lejura Rondani, Trypeta macrura Loew); U.solstitialis (Linnaeus) (= E.sonderupi Hering, U. veruata Rondani ); U.stylata (Fabricius) (= E.pia Hering, U. vulcaanica Rondani); U. terebrans (Loew) (= E. approximata Hering, T. eriolepidis Loew, E. manni Hendel). The possibility that U. quadrifasciata is a species complex is discussed; it is also suggested that U.affinis and U.jaceana represent the morphological extremes of a complex. The misuse of the name Musca stylata Fabricius in the genus Myopites Blot is noted.     

Analysis of CD36 expression on human monocytic cells and atherosclerotic tissue sections with quantum dots: investigation by flow cytometry and spectral imaging microscopy

OBJECTIVE: To demonstrate CD36 expression with quantum dots (QDs) 525 and/or 605 on human monocytic U937 cells and atherosclerotic tissue sections by means of flow cytometry (FCM) and/or confocal laser scanning microscopy (CLSM). STUDY DESIGN: U937 cells and tissue sections were analyzed by means of FCM and/or CLSM. FCM was performed, using different ultraviolet (UV) and visible (488/532 nm) excitation modes. In the visible mode, fluorescence intensities of QDs, phycoerythrin (PE) and fluorescein isothiocyanate (FITC) were compared. Three-dimensional (3-D) sequences of images were obtained by spectral analysis in a CLSM and analyzed by the factor analysis of medical image sequences (FAMIS) algorithm, providing factor curves and images. Factor images are the result of the FAMIS image processing method, which differentiates emission spectra from 3D sequences of images. In CLSM analysis, preparations are screened in a UV excitation mode to optimize the possibilities of QDs and have the benefit of 4',6-diamino-2-phenylindole or Hoechst 33342 counterstaining of nuclei. RESULTS: FCM and CLSM revealed CD36 expression by means of QDs 525 and/or 605. Fluorescence intensity of PE and of FITC was higher than that of QDs 525 and of 605. As factor curves and images show the red emission of QDs 605 only, subsequent reliable identification and localization of CD36 was obtained. CONCLUSION: QDs 525 and 605 are useful to analyze antigenic expression. Following FCM, which is well adapted to detect fluorescence emission of QDs in the UV or visible excitation mode, CLSM and subsequent spectral analysis assess more specific characterization of QD fluorescent emissions.     

Study of a therapeutic concentrate of factor VIII/vWf prepared in a closed system

An original procedure of preparation in a closed system of high purity Factor VIII concentrate is presented. Starting from cryoprecipitates, this method involves a first step of partial removal of fibrinogen by glycine precipitation (1.6 M) and a second step of Factor VIII concentration by cryoprecipitation. The yield is 16.5% of plasmatic F VIII:C (0.8 mu/ml.). Several batches of concentrates thus prepared are compared "in vitro" to 9 other commercially available concentrates from 8 different manufactories. The results show that most of the characteristics of our concentrate are within the range of specifications of other commercially available high-purity F VIII concentrate: F VIII: C activity (CRTS Lille concentrate: 25-40 U/ml.; other concentrates: 25-50 U/ml) solubility, specific activity (CRTS lille concentrate; 1.0-1.82 U F VIII:C/mg protein and 1.79-4.8 U F VIII: C/mg clottable proteins; other concentrates: 0.53-2.79 U F VIII:C/mg protein an 1.39-4.84 U F VIII:C/mg clottable proteins), isoagglutinin titers (CRTS Lille concentrate: 2-8 anti-A, 0.16 anti-B; other concentrates: 0-64 anti-A, 8-16 anti-B) F VIIIC/F VIII R: Ag ratios (CRTS Lille concentrate: 0.18-0.49; other concentrates: 0.20-0.42). Furthermore F VIII R:Ag electrophoretic mobility studied by crossed immunoelectrophoresis add F VIII R: RCo assays provide evidence that very high molecular weight multimeric forms of F VIII/vWf which support vWf activity are present in our concentrate. "In vivo" study and clinical efficacy in vWd patients confirm these results and show that our concentrate is appropriate for the treatment of patients with F VIII:C or V VIII R:RCo deficiency.     

Interactively optimizing signal-to-noise ratios in expression profiling: project-specific algorithm selection and detection p-value weighting in Affymetrix microarrays

MOTIVATION: The most commonly utilized microarrays for mRNA profiling (Affymetrix) include 'probe sets' of a series of perfect match and mismatch probes (typically 22 oligonucleotides per probe set). There are an increasing number of reported 'probe set algorithms' that differ in their interpretation of a probe set to derive a single normalized 'signal' representative of expression of each mRNA. These algorithms are known to differ in accuracy and sensitivity, and optimization has been done using a small set of standardized control microarray data. We hypothesized that different mRNA profiling projects have varying sources and degrees of confounding noise, and that these should alter the choice of a specific probe set algorithm. Also, we hypothesized that use of the Microarray Suite (MAS) 5.0 probe set detection p-value as a weighting function would improve the performance of all probe set algorithms. RESULTS: We built an interactive visual analysis software tool (HCE2W) to test and define parameters in Affymetrix analyses that optimize the ratio of signal (desired biological variable) versus noise (confounding uncontrolled variables). Five probe set algorithms were studied with and without statistical weighting of probe sets using the MAS 5.0 probe set detection p-values. The signal-to-noise ratio optimization method was tested in two large novel microarray datasets with different levels of confounding noise, a 105 sample U133A human muscle biopsy dataset (11 groups: mutation-defined, extensive noise), and a 40 sample U74A inbred mouse lung dataset (8 groups: little noise). Performance was measured by the ability of the specific probe set algorithm, with and without detection p-value weighting, to cluster samples into the appropriate biological groups (unsupervised agglomerative clustering with F-measure values). Of the total random sampling analyses, 50% showed a highly statistically significant difference between probe set algorithms by ANOVA [F(4,10) > 14, p < 0.0001], with weighting by MAS 5.0 detection p-value showing significance in the mouse data by ANOVA [F(1,10) > 9, p < 0.013] and paired t-test [t(9) = -3.675, p = 0.005]. Probe set detection p-value weighting had the greatest positive effect on performance of dChip difference model, ProbeProfiler and RMA algorithms. Importantly, probe set algorithms did indeed perform differently depending on the specific project, most probably due to the degree of confounding noise. Our data indicate that significantly improved data analysis of mRNA profile projects can be achieved by optimizing the choice of probe set algorithm with the noise levels intrinsic to a project, with dChip difference model with MAS 5.0 detection p-value continuous weighting showing the best overall performance in both projects. Furthermore, both existing and newly developed probe set algorithms should incorporate a detection p-value weighting to improve performance. AVAILABILITY: The Hierarchical Clustering Explorer 2.0 is available at http://www.cs.umd.edu/hcil/hce/ Murine arrays (40 samples) are publicly available at the PEPR resource (http://microarray.cnmcresearch.org/pgadatatable.asp http://pepr.cnmcresearch.org Chen et al., 2004).     

DNA-uracil and human pathology

Uracil is usually an inappropriate base in DNA, but it is also a normal intermediate during somatic hypermutation (SHM) and class switch recombination (CSR) in adaptive immunity. In addition, uracil is introduced into retroviral DNA by the host as part of a defence mechanism. The sources of uracil in DNA are spontaneous or enzymatic deamination of cytosine (U:G mispairs) and incorporation of dUTP (U:A pairs). Uracil in DNA is removed by a uracil-DNA glycosylase. The major ones are nuclear UNG2 and mitochondrial UNG1 encoded by the UNG-gene, and SMUG1 that also removes oxidized pyrimidines, e.g. 5-hydroxymethyluracil. The other ones are TDG that removes U and T from mismatches, and MBD4 that removes U from CpG contexts. UNG2 is found in replication foci during the S-phase and has a distinct role in repair of U:A pairs, but it is also important in U:G repair, a function shared with SMUG1. SHM is initiated by activation-induced cytosine deaminase (AID), followed by removal of U by UNG2. Humans lacking UNG2 suffer from recurrent infections and lymphoid hyperplasia, and have skewed SHM and defective CSR, resulting in elevated IgM and strongly reduced IgG, IgA and IgE. UNG-defective mice also develop B-cell lymphoma late in life. In the defence against retrovirus, e.g. HIV-1, high concentrations of dUTP in the target cells promotes misincorporation of dUMP-, and host cell APOBEC proteins may promote deamination of cytosine in the viral DNA. This facilitates degradation of viral DNA by UNG2 and AP-endonuclease. However, viral proteins Vif and Vpr counteract this defense by mechanisms that are now being revealed. In conclusion, uracil in DNA is both a mutagenic burden and a tool to modify DNA for diversity or degradation.