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  • 1
    ISSN: 1432-2242
    Keywords: Reproductive fitness ; Artificial selection ; Ethanol tolerance ; Quantitative character ; Drosophila melanogaster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The maintenance of reproductive fitness in lines subjected to artificial selection is one of the major problems in animal breeding. The decline in reproductive performance has neither been predictable from heritabilities and genetic correlations, nor have conventional selection indices been adequate to avoid the problem. Gowe (1983) has suggested that the heritabilities of reproductive traits are non-linear, with heritabilities being higher on the lower fitness side. Consequently, he has predicted that culling on reproductive fitness in artificial selection lines will be effective in preventing the usual declines in fitness. An experimental evaluation of Gowe's prediction has been carried out by comparing fitnesses of replicated lines of three treatments: selection for increased inebriation time without culling on fitness (HO), selection for inebriation time with culling of 20% (4/20) of selected females on reproductive fitness (HS), and unselected controls (C). Response to selection for inebriation time in the two selection treatments was similar. After 25 generations, the competitive index, a measure of reproductive fitness, was significantly lower in the HO treatment than the HS treatment, while the HS treatment did not differ from the control lines or the base population. These results demonstrate for the first time that culling on reproductive fitness in selection lines can be used to prevent the usual decline in reproductive performance.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2242
    Keywords: Long-term selection ; Residual genetic variability ; Heritability ; Abdominal bristle number ; Drosophila melanogaster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Six replicate lines of Drosophila melanogaster, which had been selected for increased abdominal bristle number for more than 85 generations, were assayed by hierarchical analysis of variance and offspring on parent regression immediately after selection ceased, and by single-generation realised heritability after more than 25 generations of subsequent relaxed selection. Half-sib estimates of heritability in 5 lines were as high as in the base population and much higher than observed genetic gains would suggest, excluding lack of sufficient additive genetic variance as a cause of ineffective selection in these lines. Also, there was considerable diversity among the six lines in composition of phenotypic variability: in addition to differences in the additive genetic component, one or more of the components due to dominance, epistasis, sex-linkage or genotype-environment interaction appeared to be important in different lines. Even after relaxed selection, single-generation realised heritabilities in four lines were as high as in the base population. As a large proportion of total genetic gain must have been made by fixation of favourable alleles, the compensatory increase of genetic variability has been sought in a genetic model involving genes at low initial frequencies, enhancement of gene effects during selection and/or new mutations.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2242
    Keywords: Long-term selection ; Relaxed selection ; Reverse selection ; Dominance of bristle number genes ; Drosophila melanogaster
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Reverse and relaxed selection were carried out in sublines which were derived from six replicate lines of Drosophila during 86–89 generations of selection for increased abdominal bristle number, and the reverse selection sublines were reciprocally crossed with selection lines of their origin. The results of serial relaxed selection initiated at different generations of selection confirm that the accelerated responses observed in the selection lines were largely due to deleterious genes, particularly lethals, with large effects on the selected character. The decline in mean bristle number under relaxed selection was not much different between crowded and uncrowded relaxed sublines. Reverse selection initiated at generation 57 was very effective, though it failed to bring the mean back to the base population level, and the genetic differences between replicate sublines (two from each of the six lines) indicate that low bristle number genes were probably rare in the selection lines. The genes which were still segregating after 57 generations of selection, on the average, did not show any directional dominance. The contribution of the X-chromosome to selection response was proportional to its chromosome length.
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  • 4
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0935-6304
    Keywords: Cyclic carbonates ; thermal stability ; chemical stability ; gas phase chromatography ; liquid phase chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---No abstract
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1040-7685
    Keywords: microcolumn liquid chromatography ; liquid chromatography/mass spectrometry ; temperature programming ; optimization methods ; fatty acids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A temperature-programmed microcolumn liquid chromatography/mass spectrometry (LC/MS) system has been developed as a practical alternative to conventional solvent-programmed LC/MS. Good reproducibility of solute retention was achieved in a specially modified oven that permitted linear temperature programming between 40 and 100°C at rates of 0.1 to 0.5°C min-1. Through theoretical modelling studies performed under isocratic and isothermal conditions, the optimum separation under temperature-programmed conditions was rapidly and accurately predicted. This method enabled the complete resolution of saturated and unsaturated fatty acids in a fish oil dietary supplement with identification from their characteristic fragmentation patterns under electron-impact MS conditions. The mass spectra from the LC/MS system correlated very well with those from a standard reference library to facilitate spectral searching methods.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0887-3585
    Keywords: crystals ; bacterial esterase ; X-ray diffraction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Large crystals of arylesterase from Pseudomonas fluorescens have been grown at room temperature using ammonium sulfate as a precipitant. They grow to dimensions of 0.7 × 0.7 × 0.6 mm3 within a month. The crystals belong to the trigonal space group P31 (or P32), with unit cell dimensions of a= 147.12 Å and c= 131.08 Å. The asymmetric unit seems to contain six molecules of dimeric aryles-terase, with corresponding crystal volume per protein mass (VM) of 2.53 Å3/Da and solvent fraction of 51.5% by volume. The crystals diffract to at least 2.2 Å Bragg spacing when exposed to X-rays from a rotating-anode source. X-ray data have been collected to 2.9 Å Bragg spacing from native crystals. © 1993 Wiley-Liss, Inc.
    Additional Material: 1 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A vacuum ultraviolet photolysis of C2H5Br at 147 nm was studied over a pressure range of 0.5-50 torr at 298 K. The effects of additives He and NO were also investigated.The principal reaction products were found to be C2H4 and C2H6, with lesser yields of CH4 and C2H2. With increasing pressure the product quantum yields Φi of C2H4, CH4, and CH2H6 remained constant, while that of C2H2 decreased from 0.03 to almost 0. The effect of He as an additive was found to be extremely small on the quantum yields of the major products. Addition of NO completely suppresses the formation of CH4, C2H2, and C2H6, and reduces partially the production of C2H4. The primary processes appear to involve two electronically excited states. One state mainly yields C2H4 by molecular elimination of HBr and is thought to be due to a Rydberg transition. The other state decomposes to C2H5 and Br radicals by C—Br bond fission. These two competitive reaction modes contribute to the photodecomposition in proportions of 50% and 50%. The extinction coefficient for C2H5Br at 147 nm and at 298 K has been determined as ∊ = (1/PL) In(Io/It) = 712 ± 7 atm-1 · cm-1.
    Additional Material: 2 Ill.
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  • 9
    ISSN: 0959-8103
    Keywords: poly(esterurethane) ; copolyamide segments ; thermal and mechanical properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Thermoplastic polyurethane elastomers (TPUs) from diol-terminated poly(ethylene adipate) (PEA), 1,4-butanediol (BD) and 4,4′-diphenylmethane-diisocyanate (MDI) were modified by copolymerizing with diamine-terminated nylon-6/6,6 copolyamide (CPA) oligomers. The effects of content and molecular weight of CPA segments on the thermal and mechanical properties of TPU were studied. PEA segments showed enhanced crystallization when some of the hard segments were replaced by CPA segments, showing weaker CPA-PEA interaction. The crystallinity of the hard segments was reduced, probably due to some interaction and phase mixing between hard and CPA segments. The modulus of TPU also decreased, more markedly with CPA segments of higher molecular weight.
    Additional Material: 7 Ill.
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  • 10
    ISSN: 1042-7147
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Small-angle neutron scattering studies have been used to clarify several aspects of the internal structure of latexes and subsequent film formation modes. This paper reviews work both around the world and at Lehigh University on those subjects. Two points have been made clear: (1) The appearance of core-shell phenomena in latexes depends on the size of the polymer chain to that of the latex particle; the phenomenon is most marked when the radius of gyration of the chain is about one fifth as big as the latex radius. (2) Strength build-up during film formation depends on the extent of interdiffusion of the chains. For moderate molecular weights, interdiffusion distances of one radius of gyration yield maximum strength. For both moderate (250,000 g/mol) and high (2,000,000 g/mol) molecular weights, full strength was achieved in two hour's annealing time at 144°C.
    Additional Material: 11 Ill.
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