高粱不同品种的核型分析

我国高粱的种植,不仅面积大,而且品种众多,农艺性状差异显著。有关高粱核型的分析,部分品和已有报道'－"。为了更多地了解不同品种的核型,从而为研究高粱的进化和遗传育种等提供必要的细胆学依据,作者对4个高粱品种的核型进行了G一显带分析,报道如下。1材料和方法本实验所用材料,分别由吉林省农科院和河南省农科院提供。种子于25℃萌发,待根长Icm左右时,按宋运淳"'等修改的ASG法制片,核型分析按李极学"'等建议的标准进行。2结果与分析"郑粱2号"、"甜杆G"、"竹叶青"和"忻粱7号"的细胞有丝分裂中期相与相应的核型见图版1：A－…     

蒙古苍耳核型分析

首次对蒙古苍耳染色体数目及核型进行了研究,结果表明,染色体数目２ｎ＝３６,核型公式为Ｋ（２ｎ）＝３６＝２６ｍ＋２ｍ（ｓａｔ）＋８ｓｍ．与苍耳的核型进行比较,认为蒙古苍耳的核型比苍耳的原始。     

RISK OF POPULATION EXTINCTION FROM FIXATION OF NEW DELETERIOUS MUTATIONS

The fixation of new deleterious mutations is analyzed for a randomly mating population of constant size with no environmental or demographic stochasticity. Mildly deleterious mutations are far more important in causing loss of fitness and eventual extinction than are lethal and semilethal mutations in populations with effective sizes, N_e, larger than a few individuals. If all mildly deleterious mutations have the same selection coefficient, s against heterozygotes and 2s against homozygotes, the mean time to extinction, , is asymptotically proportional to for 4N_es > 1. Nearly neutral mutations pose the greatest risk of extinction for stable populations, because the magnitude of selection coefficient that minimizes is about ? = 0.4/N_e. The influence of variance in selection coefficients among mutations is analyzed assuming a gamma distribution of s, with mean and variance . The mean time to extinction increases with variance in selection coefficients if is near ?, but can decrease greatly if is much larger than ?. For a given coefficient of variation of , the mean time to extinction is asymptotically proportional to for . When s is exponentially distributed, (c = 1) is asymptotically proportional to . These results in conjunction with data on the rate and magnitude of mildly deleterious mutations in Drosophila melanogaster indicate that even moderately large populations, with effective sizes on the order of N_e = 10³, may incur a substantial risk of extinction from the fixation of new mutations.     

INTERACTIONS BETWEEN NITRATE UPTAKE AND NITROGEN FIXATION IN CONTINUOUS CULTURES OF THE MARINE DIAZOTROPH TRICHODESMIUM (CYANOBACTERIA)1

Diazotrophic cyanobacteria can take up combined nitrogen (nitrate, ammonium, amino acids, dissolved organic nitrogen) from solution, but the interaction between N₂ fixation and uptake of combined nitrogen is not well understood. We studied the effects of combined nitrogen ) additions on N₂ fixation rates in the cyanobacterium Trichodesmium erythraeum (IMS‐101) maintained in continuous culture in an N‐free medium (YBCII) and a 12:12‐h light:dark cycle. We measured acetylene reduction rates, nutrient concentrations, and biomass throughout the 12 h of illumination after the addition of nitrate (0.5–20 μM) at the start of the light period. Compared with unamended controls, Trichodesmium showed strong inhibition of acetylene reduction (up to 70%) in the presence of , with apparent saturation of the inhibition effect at an initial concentration of approximately 10 μM. The inhibition of acetylene reduction persisted through much of the light period as concentration in the culture vessel decreased. Recovery of N₂ fixation was observed late in the light period in cultures amended with low concentrations of (<5 μM) when ambient concentrations had decreased to 0.3–0.4 μM in the culture vessel. Nitrate uptake accounted for as much as 86% of total N uptake and, at the higher treatment concentrations, more than made up for the observed decrease in N₂ fixation rates. We conclude that Trichodesmium can obtain significant quantities of N through uptake of nitrate and does so in preference to N₂ fixation when sufficient is available.     

活血莲的核型分析

对活血莲的染色体数目及核型进行了研究,结果表明,活血莲的染色体数目为２ｎ＝６０,其核型公式为２ｎ＝２ｘ＝６０＝４６ｓｍ＋１２ｓｔ＋２ｍ。没有观察到带随体的染色体。     

串叶松香草的核型研究

串叶松香草Silphiura perfoliatum L.系菊科(Compositae)松香草属(SilphiumL.)多年生宿根草本植物,原产北美洲。1979年由中国科学院植物研究所北京植物园首次从朝鲜引进我国,1980年引种我所栽培,通过几年的试验观察表明:串叶松香草是一种高产、质优、适应性强的饲料作物,近年来,我省广泛发展和应用。据文献报     

韭菜的小孢子四分体微核和核型的初步研究

本文研究了昆明栽培的韭菜的小孢子染色体数目和核型,多数小孢子的染色体数目ｎ＝１６,少数是非整倍体,核型公式为ｎ＝２ｘ＝１６＝１４ｍ＋２ｓｔ（ＳＡＴ）。同时观察了韭菜的育性和小孢子四分体微核情况,育性和四分体微核率分别为４８％、２３６％。上述结果说明韭菜的核型与前人曾报道过的韭菜的核型一样是同源四倍体。     

FIXATION OF SLIGHTLY BENEFICIAL MUTATIONS: EFFECTS OF LIFE HISTORY

Recent studies of rates of evolution have revealed large systematic differences among organisms with different life histories, both within and among taxa. Here, we consider how life history may affect the rate of evolution via its influence on the fixation probability of slightly beneficial mutations. Our approach is based on diffusion modeling for a finite, stage‐structured population with stochastic population dynamics. The results, which are verified by computer simulations, demonstrate that even with complex population structure just two demographic parameters are sufficient to give an accurate approximation of the fixation probability of a slightly beneficial mutation. These are the reproductive value of the stage in which the mutation first occurs and the demographic variance of the population. The demographic variance also determines what influence population size has on the fixation probability. This model represents a substantial generalization of earlier models, covering a large range of life histories.     

三种药用车前的染色体数目和核型的研究

<正> 车前为常用中药材,《神农本草经》和明李时珍的《本草纲目》中列为上品,以干燥全草及种子入药,有清热、明目、利尿、止泻、降低血压和镇咳祛痰等功效。 本文报道了作为“车前”中药材的三种车前属Plantago L.植物:大车前P. major L.车前P. aslatica L. 和平车前P. depressa Willd.染色体数目和核型的资料,旨在为探讨车前属内的分类和进化及为提高车前中药材的产量和质量的研究提供必要的细胞学资料。     

活血莲的核型分析

对活血莲的染色体数目及核型进行了研究,结果表明;活血莲的染色体数目为2n=60,其核型公式为2n=2x=60=46sm+12st+2m,没有观察到带随体的染色体。     

蒙古苍耳核型分析

首次对蒙古苍耳(Xanthium mongolicum Kitag.)染色体的数目及核型进行了研究,结果表明,染色体数目2n=36,核型公式为K(2n)=36=26m+2m(sat)+8sm.与苍耳(Xanthium sibiricum Patrin.)的核型进行比较,认为蒙古苍耳的核型比苍耳的原始。     

皱纹盘鲍的染色体研究

本文报道皱纹盘鲍的染色体制备方法及核型分析结果。皱纹盘鲍的2n=36,可配为18对,中央着丝点(M)的11对,即1,3,6,7,9,11,12,13,14,16,17号染色体。亚中央着丝粒(Sm)的7对,即2,4,5 8,15,18号染色体,NF=72。染色体的长度呈连续递变。其中相对长度最长的1号染色体为7.09,最短的18号染色体4.11,单倍体总长687.05。     

北方几种小浆果植物的核型研究

对悬钩子属、醋栗属、越桔属、沙棘属、接骨木属和五味子属等６属１２种小浆果植物的染色体数目和核型进行了研究。其中绿叶悬钩子、牛迭肚和刺果茶Ｂｉａｏ的染色体数目为首次报道。截止目前,关于小浆果植物的核型资料报道甚少。     

扬子毛茛和石龙芮的核型研究

报道了浙江省常见的２种毛茛属植物－扬子毛茛和石龙芮的染色体资料,扬子毛茛体细胞染色体数目２ｎ＝３２,核型组成;Ｋ（２ｎ）＝４ｘ＝３２＝１６ｍ＋８ｓｍ＋８ｓｔ。石龙芮体细胞染色体数目２ｎ＝３２,核型组成;Ｋ（２ｎ）＝４ｘ＝３２＝８ｍ＋２４ｓｍ。     

睡莲科的核型分析及其分类学位置的探讨

本文对睡莲科6属6种代表植物的核型进行了研究,并探讨了它的分类学位置。结果如下：莲2n＝16=9sm+4m+3st;王莲2n＝24=8sm+8m+8T,蓝睡莲2n＝28,可配成14对,染色体小,第l号染色体上有2条随体;萍蓬草2n＝34＝18m+16sm;芡实2n=58,可配成29对,染色体小,第l号染色体有2条随体,莼菜2n＝72,可配成36对,染色体按大小可分成大,中、小三个类别。除莲外,其它5种植物的核型为首次报道。莼菜的体细胞染色体数目2n＝72和国外报道的2n＝80不相一致。莲的染色体以及形态学特征和其它睡莲科分类群显著不同,可将其从睡莲科中独立出来,并成立莲科和莲目。原归属于睡莲科的分类群仍组成睡莲目,并分别置于莼菜科和睡莲科。     

THE FOUNDING OF A NEW POPULATION OF DARWIN'S FINCHES

We report the natural colonization of the small Galápagos island Daphne Major by the large ground finch (Geospiza magnirostris). Immigrants of this species were present in every year of a 22-yr study, 1973–1994. Typically they arrived after a breeding season and left at the beginning of the next one. Geospiza magnirostris bred on the island for the first time in the exceptionally wet El Niño year of 1982–1983, and bred in all subsequent years except drought years. In agreement with theoretical expectations the frequency of inbreeding was unusually high. Pronounced fluctuating asymmetry in tarsus length, together with slightly reduced breeding success of inbreeding pairs, suggests a low level of inbreeding depression. Despite this, the population increased from 5 breeding individuals in 1983 to 20 breeding individuals in 1992, and probably more than twice that number in 1993, largely through recruitment of locally born birds.     

植物群落种群分布格局研究的新方法

本文给出一种研究植物群落种群分布格局的新方法。该方法与英国著名生态学家Greig-Smith提出的“邻接格子样方法”相比较,具有如下优点: 1.用计算机算出的结果,具有令人满意的精度。当计算完毕后,机器能打印输出植物种群斑块大小、斑块在样地平面上分布的状况,样地上某种植物斑块的总面积,种群个体的总数等有关信息。 2.适用于天然植物群落种群分布格局的研究。 本文讨论了处理数据时采用的计算公式,所依据的数学原理以及如何确定输出界限(舍入界限)等问题。 此外,文中还叙述了用该法对随机相嵌几何斑块图形,人工模拟草地样方进行处理的过程和计算结果分析。 源程序是用BASIC语言编制的。     

FIXATION OF MUTATORS IN ASEXUAL POPULATIONS: THE ROLE OF GENETIC DRIFT AND EPISTASIS

We study the evolutionary dynamics of an asexual population of nonmutators and mutators on a class of epistatic fitness landscapes. We consider the situation in which all mutations are deleterious and mutators are produced from nonmutators continually at a constant rate. We find that in an infinitely large population, a minimum nonmutator‐to‐mutator conversion rate is required to fix the mutators but an arbitrarily small conversion rate results in the fixation of mutators in a finite population. We calculate analytical expressions for the mutator fraction at mutation‐selection balance and fixation time for mutators in a finite population when the difference between the mutation rate for mutator and nonmutator is smaller (regime I) and larger (regime II) than the selection coefficient. Our main result is that in regime I, the mutator fraction and the fixation time are independent of epistasis but in regime II, mutators are rarer and take longer to fix when the decrease in fitness with the number of deleterious mutations occurs at an accelerating rate (synergistic epistasis) than at a diminishing rate (antagonistic epistasis). Our analytical results are compared with numerics and their implications are discussed.