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John K. Raper 《Theoretical population biology》1983,24(2):192-211
A general model is analyzed in which arbitrarily frequency-dependent selection acts on one sex of a diploid population with several alleles at one locus, as a result of viability or mating-success differences. The existence of boundary and polymorphic equilibria is examined, and conditions for local stability, internal and external, are obtained. The status of Hardy-Weinberg approximations in studying stability and approach to equilibria is also considered. The general principles are then applied to two specific models: one where genotypes fall into two phenotypic classes; and one with a hierarchy of dominance where viability and sexual selection are opposed. In the latter case it is found that, of all the equilibria present, there is one and only one which could possibly be stable: the existence of a unique globally stable equilibrium might then be inferred. 相似文献
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C. Cuoco G. Gimelli F. Pasquali L. Poloni O. Zuffardi P. Alicata G. Battaglino F. Bernardi R. Cerone M. Cotellessa A. Ghidont S. Motta 《Human genetics》1982,61(1):3-7
Summary Five females with duplication of the short arm of one chromosome 9 are reported, one tetrasomic and four trisomic for 9p. The tetrasomy is due to an isochromosome 9p while the trisomies are due in one case to an intrachromosomal duplication present in lymphocytes but not in fibroblasts, two are secondary to translocations with chromosomes 22 and 13 respectively, and one is a mosaic with a cell line with an additional deleted chromosome 9 present in lymphocytes and fibroblasts. This analysis indicates that duplications 9p may result in impairment of ovarian function. The phenotypic differences between trisomy and tetrasomy 9p are discussed. 相似文献
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Henri J. Dumont Ionel Miron Ugo Dali'asta Wilfrida Decraemer Christine Glaus Daniel Somers Henri J. Dumont 《International Review of Hydrobiology》1973,58(1):33-60
Four mountain lakes were studied. Two are eutrophic, one is mesotrophic and one is oligotrophic. The first three have a well-developed phyto- and zooplankton, with a relatively high diversity index. There are differences between the faunas that may be ascribed to differences in surface, depth, altitude and also to biological phenomena such as interspecies competition. The Ifni Lake is a genuine high-mountain lake, subject to severe environmental conditions. It has a very simple food chain: there is only one species of algae, an unicellular blue-green, one copepod species, one rotifer and one fish. In general some features of a definite interest for fundamental limnology were found: the presence of a pelagic Rhabdocoelid in Dayat Ifrah, some particularities in the vertical distribution of a number of plankton species, the existence of a layer of relatively warm water near the bottom of Lake Ifni. The latter is explained by a strong bottom current which flows through the lake between its phreatic in- and outlets. Finally, stress is laid on the under-exploitment of Moroccon inland waters with respect to a freshwater fishery. Yet, perspectives are good and some suggestions are forwarded. 相似文献
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BENJAMIN C. STONE F.L.S. 《Botanical journal of the Linnean Society. Linnean Society of London》1970,63(2):97-131
The sections of the genus Pandanus which occur in Madagascar are the main subject of this paper. There are 75 species in the island, of which all, or all but one, are endemic. They can be grouped into 12 sections, of which six are endemic, and one is a local endemic subsection. The other sections occur elsewhere, mainly in Africa, but two to the east. A key to the sections is given, and a discussion of field recognition characters is included. One new section and one new subsection are proposed. New lectotypifications for Sections Sussea and Vinsonia are suggested. The Madagascar species of Thouars are discussed. Finally a resume of some recent collections is presented. 相似文献
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羊草大、小孢子发生与雌、雄配子体发育的观察 总被引:5,自引:0,他引:5
利用常规石蜡制片技术研究了羊草大、小孢子发生及雌、雄配子体发育过程。主要结果是:(1)花药壁由4层结构组成,最外层为表皮,其次为药室内壁,1层中层,最内层绒毡层为分泌型;(2)小孢子母细胞减数分裂过程中的胞质分裂为连续型,四分孢子为左右对称型;(3)成熟花粉粒为3细胞型,具单萌发孔;(4)羊草为单子房、单胚珠,双珠被、薄珠心、倒生型胚珠,大孢子母细胞减数分裂形成线型或T型排列的4个大孢子;合点端大孢子具功能;(5)具有双孢原,双大孢子母细胞、双大孢子四分体和双胚囊的情况;(6)胚囊发育为蓼型,反足细胞经无丝分裂形成4~6个细胞的反足细胞群;(7)同一朵花中,前期雄蕊的发育早于雌蕊的发育,后期当花粉成熟时,雌配子体也达到成熟,雌雄蕊发育趋于同步。 相似文献
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L. R. CLEVELAND 《The Journal of eukaryotic microbiology》1958,5(1):47-62
SYNOPSIS. The role of eleven different types of achromatic figures in chromosomal movement of Barbulanympha is analyzed. When only one pole is present, no chromosomes are ever connected with it, and hence they do not move. The chromosomes go through their usual life cycle including pairing, but remain in the parent nucleus, which, of course, does not divide. When two poles are present with only one pole near the nucleus, the poles, which are the distal ends of the elongate centrioles, do not cooperate in the formation of a central spindle and the chromosomal behavior is just as if there were only one pole—no movement. The same is true when more than two poles are present with only one near the nucleus.
Unless a central spindle is present, movement of chromosomes never occurs. However, when many central spindles are present, sister chromosomes may separate and move to poles which are not directly connected by a central spindle. In other words, sisters may separate without moving along a central spindle.
In binucleate cells with one central spindle the chromosomes of one nucleus move to the poles, but those of the other do not. Movement always occurs in the nucleus that has its nuclear membrane depressed by the central spindle. When two or more central spindles are present, the chromosomes of both nuclei may move to the poles. 相似文献
Unless a central spindle is present, movement of chromosomes never occurs. However, when many central spindles are present, sister chromosomes may separate and move to poles which are not directly connected by a central spindle. In other words, sisters may separate without moving along a central spindle.
In binucleate cells with one central spindle the chromosomes of one nucleus move to the poles, but those of the other do not. Movement always occurs in the nucleus that has its nuclear membrane depressed by the central spindle. When two or more central spindles are present, the chromosomes of both nuclei may move to the poles. 相似文献
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中国盾脸姬蜂亚科一新种及一新记录(膜翅目:姬蜂科)盛茂领章英(林业部森林病虫害防治总站沈阳110034)1995-04-20收稿,1996-01-17收修改稿·92·黄脸姬蜂属ChorinaeusHolmgren,1856和突唇姬蜂属Ischyroc... 相似文献
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A two-stage design is proposed to choose among several experimental treatments and a standard treatment in clinical trials. The first stage employs a selection procedure to select the best treatment, provided it is better than the standard. The second stage tests the hypothesis between the best treatment selected at the first stage (if any) and the standard treatment. All the treatments are assumed to follow normal distributions and the best treatment is the one with the largest population mean. The level and the power are defined and they are used to set up equations to solve unknown first stage sample size, second stage sample size, and procedure parameters. The optimal design is the one that gives the smallest average sample size. Numerical results are presented to illustrate the improvement of one design as compared to existing one stage design. 相似文献
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W Ansorge H Voss U Wirkner C Schwager J Stegemann R Pepperkok J Zimmermann H Erfle 《Journal of biochemical and biophysical methods》1989,20(1):47-52
Novel Sanger dideoxy sequencing with only one fluorescent dye label for the four bases of one clone and sequence determination in two lanes on polyacrylamide gel is presented, loading A greater than G in one lane and T greater than C in the other. Sequencing reactions for the two bases in each lane are carried out in one tube. At present the ratio of ddATP:ddGTP and ddTTP:ddCPT is set to 5:1 in the two tubes. Distinction between the two bases in one lane is done by comparing the different magnitudes of the peaks. This method increases the capacity since more clones may be run simultaneously on one gel, while keeping the reliability and simplicity that comes with the use of only one fluorescent dye for the four bases of one clone. At present about 200 bases are determined with the one-dye two-lane method on the EMBL's automated fluorescent DNA sequencer, using T7 DNA polymerase. The error rate in the deduced sequence is about 1%. The technique is used for the determination of overlaps in mapping projects. In principle, it is possible to determine the sequence with one dye in only one lane on the gel by choosing the proper ddNTP ratios for all four bases, carrying out reactions in one tube and applying the product in one lane, but the error rate for this one-lane method seems too high at present and further improvements in the uniformity of peaks obtainable with the T7 DNA polymerase or other enzymes are required. 相似文献
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Most models of dynamics of infectious diseases have assumed homogeneous mixing in the host population. However, it is increasingly
recognized that heterogeneity can arise through many processes. It is then important to consider the existence of subpopulations
of hosts, and that the contact rate within subpopulations is different than that between subpopulations. We study models with
hosts distributed in subpopulations as a consequence of spatial partitioning. Two types of models are considered. In the first
one there is direct transmission. The second one is a model of dynamics of a mosquito-borne disease, with indirect transmission,
and applicable to malaria. The contact between subpopulations is achieved through the visits of hosts. Two types of visit
are considered: a first one in which the visit time is independent of the distance travelled, and a second one in which visit
time decreases with distance. There are two types of spatial arrangement: one dimensional, and two dimensional. Conditions
for the establishment of the disease are obtained. Results indicate that the disease becomes established with greater difficulty
when the degree of spatial partition increases, and when visit time decreases. In addition, when visit time decreases with
distance, the establishment of the disease is more difficult when the spatial arrangement is one dimensional than when it
is two dimensional. The results indicate the importance of knowing the spatial distribution and mobility patterns to understand
the dynamics of infectious diseases. The consequences of these results for the design of public health policies are discussed. 相似文献
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长白山天蛾科昆虫区系特点及地理分布 总被引:1,自引:0,他引:1
调查研究表明:长白山自然保护区有天蛾科昆虫31种,隶属5个亚科19属。其中白须天蛾Kentrochrysalis sieversiAlpheraky、女贞天蛾K.streckeriStaudinger为长白山新记录,黄脉天蛾AmorphaamurensisStaudinger为优势种。绝大多数天蛾种类是单带种,仅分布阔叶红松林带,只有黄脉天蛾为多带种。天蛾成虫活动期为5月下旬~8月中旬,种群数量最多时间为6月~7月。昆虫区系主要起源于古北区,区系以东方成分为主,其次是欧洲-西伯利亚成分,亦有一定数量中亚细亚或印度-马来西亚成分。 相似文献
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The present study examines the indispensability of a nucleus or nucleus-deriving factors in the induction of cleavage in Xenopus eggs by testing cleavage in Xenopus eggs fertilized with ultraviolet (UV)-damaged sperm and deprived of the female nucleus. These eggs, which contain only one UV-damaged nucleus with one set of centrioles, undergo unique cleavages. Cleavage takes place in only one of the two blastomeres formed by the immediately preceding cleavage. Histologically, only one nucleus, which does not appear to be organized into typical chromosomes, is found in one of the two blastomeres formed by the immediately preceding cleavage. The typical bipolar spindle and the diastema, or a slit of astral rays, are formed in the blastomere that contains the nucleus. By contrast, only asters lacking the spindle and the diastema are formed in the remaining blastomeres, which do not contain a nucleus. The same results are obtained in eggs that contain two UV-damaged nuclei with one set of centrioles. In these eggs, cleavage appears to occur in one or two blastomeres that contain either or both of the nuclei and one bipolar spindle. In eggs that contain one intact and one UV-damaged nuclei, cleavage takes place quite normally with each blastomere containing one nucleus or one set of chromosomes as well as one bipolar spindle. Thus, there is a very close correlation between the presence of a nucleus and the formation of the mitotic spindle, the diastema and the cleavage furrow in the blastomeres of Xenopus embryos. We conclude that the presence of a nucleus or nucleus-deriving factors is indispensable for the formation of the bipolar spindle, the diastema and the cleavage furrow in the blastomeres of the Xenopus embryos. 相似文献
14.
Morphological Aspects of Ciliary Motility 总被引:5,自引:0,他引:5
Peter Satir 《The Journal of general physiology》1967,50(6):241-258
In Elliptio complanatus lateral cilia, two distinct patterns of filament termination can be discerned. In one case, all nine filaments are present and all are single; in the second, at least one filament is missing but doublets are still present. These probably represent different configurations within one cilium in different stroke positions; to get from one to the other, some peripheral filaments must move with respect to others. The data are consistent with the hypothesis that the filaments themselves do not change length, but rather slide past one another to accommodate increasing curvature. The bent regions of the cilium are in the form of circular arcs. In a few cases, apparent displacement of filaments at the tip (Δl) can be shown to be accounted for if we assume that all differences are generated within these arcs. The displacement per degree of bend is 35 A. Regions of bent arc are initially confined to the base of the cilium but move up the shaft as straight regions appear below them. From the relationship between arc length and radius of curvature, a shaft length that is the unit that initially bends and slides may be defined. Quantal displacements of the length of one 14S dynein may perhaps occur at sites between filaments at opposite sides of such a unit as sliding occurs. 相似文献
15.
心菌蚊属Cordyla Meigen生活于肉质真菌Russula属及地下真菌Rhizopogon属,主要取食菌柄基部,形成小而致密的白丝茧,在地下化蛹。仅分布于全北区,已知欧洲20种,新北区10种。本文报道中国心菌蚊属1新种和1新纪录种,模式标本保存于浙江林学院昆虫标本室。本属为中国新纪录属。北方心菌蚊,新种Cordyla borealisa Wu,sp.nov.(图1~3)雄翅长2.9~3.6m 相似文献
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Lake Kotto is a shallow crater lake, sometimes weakly stratified, and with a dense phytoplankton dominated by blue-green algae. The ecology of Lake Kotto and the similar, smaller lake Mboandong is described in relation to the feeding biology of their fishes. Of the five species of cichlids in Lake Kotto only one is endemic. Two are phytoplankton-feeders, one takes invertebrates as well as phytoplankton, one feeds mainly on chironomid larvae, and one preys on vertebrates as well as on invertebrates. The three phytoplanktivores are the main species eaten by man. One species of Clarias and one of Barbus also occur in Lake Kotto; and in the associated streams are four species of cyprinodont fishes. The fish fauna of Mboandong consists of three species of cichlids and two cyprinodonts, all known from the Kotto system. We contrast Lake Kotto with the oligotrophic lake Barombi Mbo, and conclude that Lake Kotto would probably be less sensitive to human interference than would Barombi Mbo. 相似文献
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Deinococcus radiodurans, although a gram-positive bacterium, has a complex cell wall with multiple layers and associates to this structural particularity, a quite unusual lipid composition for gram-positive bacteria. The conventional phospholipids (phosphatidyl ethanolamine, phosphatidyl choline, phosphatidyl glycerol...) are absent. Among the nine polar lipids detected in the R1 Anderson strain, three are glycolipids only one is a phospholipid, the other ones are glycophospholipids. One of the latter compounds contains one free amino group. Analysis by aminoacid autoanalyser enables to identify glucosamine in one glycolipid and in two glycophospholipids. Sugar analysis by gas-liquid chromatography after acid methanolysis and trifluoroacetylation, reveals the occurrence of N-acetyl glucosaminyl residues in one glycolipid and in one phospholipid. The following identification for the two lipids of D. radiodurans is proposed: phosphatidyl glucosaminyl glycerol and phosphatidyl N-acetyl glucosaminyl glycerol. 相似文献
19.
Summary We present a modification of double indirect immunofluorescence in which we used four antibodies raised in three species to visualize two different antigens. The procedure, which relies on dual recognition of a secondary antibody, requires that one primary antibody and one of the secondary antibodies be raised in the same species. As the two secondary antibodies are conjugated to two different fluorochromes, both of the antigens studied are visualized with one light filter while only one antigen is displayed with another filter. This, in turn, allows more efficient comparison of the distribution of the two antigens in a single field or photograph than is possible by comparing two fields or photographs by conventional double staining. The method is especially useful for determining possible co-localization of two cellular structures. We illustrate the method in adrenal cells in which mitochondria and intermediate filaments are seen to be co-localized. 相似文献