Relationship between heterosis and heterozygosity at marker loci: a theoretical computation

Summary In this paper we have studied the linear correlation between a genetic distance index between two parent lines (based on marker loci information) and the heterosis observed in the F₁ hybrid from the two lines, for a quantitative character (determined by several loci, or QTL). Theoretical computations of the correlation coefficient () between the distance index and the heterosis were made, assuming the biallelic model (defined by Fisher). When the alleles at both marker loci and QTL are equally distributed among the whole population of considered lines, the coefficient is a function of the squares of linkage disequilibria between alleles at marker loci and alleles at QTL. The QTL that are not marked by marker loci and marker loci that do not mark any QTL play symmetrical roles and can decrease greatly. We conclude that the prediction of F₁ hybrid heterosis based on marker loci would be more efficient if these markers were selected for their relationship to the alleles implicated in the heterotic traits considered.     

Attraction of Aedes aegypti II. Velocity of reaction to host with and without additional carbon dioxide

The velocity with which Aedes aegypti (L.) reacted to odors from a human arm was the same with and without additional carbon dioxide, and was found to increase asymptotically. The derivative dy/dx=–bX_ln described the velocity of response and was not different from the derivatives of the actual data. CO₂ may exert its main effect within the central nervous system.

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Zusammenfassung Die Geschwindigkeit, mit der Aedes aegypti auf den Geruch eines menschlichen Armes reagierte, war mit und ohne Kohlendioxyd-Zusatz die gleiche und nahm asymptotisch zu. Die Ableitung dy/dx=–bX_ln beschreibt die Geschwindigket der Reaktion und weicht von der Ableitung der aktuellen Versuchsdaten nicht ab. CO₂ mag seine Hauptwirkung innerhalb des Zentralnervensystems entfalten.

     

Increase of plasma membrane oxidoreductase activity is not correlated with the production of extracellular Superoxide radicals in human Namalwa cells

Summary We have considered the regulatory interrelationship of the plasma membrane oxidoreductase (PMOR) system and the mitochondrial respiratory capacity of human Namalwa (lymphoblastoid) cells. To this end, we made use of mitchondrially respiratory competent (⁺) cells and ⁰ cells, which lack mitochondrial DNA (mtDNA) and consequently mitochondrial respiratory activity. NADH-fer-ricyanide reductase activity of the PMOR system is increased 3-fold in ⁰ Namalwa cells compared to ⁺ cells. It is also shown for the first time that addition of coenzyme Q₁₀ and coenzyme Q₁₀-ana-logues, which can rescue ⁰ Namalwa cells in the absence of pyravate, gives rise to a further 2–3-fold increase in plasma membrane NADH-ferricyanide reductase activity. These systems were examined to determine if there exists a correlation between the regulation of the PMOR system and extracellular Superoxide radical formation as measured with the fluorescence probe L-012. No correlation was found between NADH-ferricyanide reductase activity and extracellular Superoxide radical production. PMOR function in cellular proliferation appears therefore not to involve extracellular Superoxide radical production.Abbreviations CoQ₁₀ coenzyme Q₁₀ - EtBr ethidium bromide - HCO-60 polyoxyethylated hydrogenated castor oil - HEPES 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid - mtDNA mitochondrial DNA - L-012 8-amino-5-chloro-7-phenylpyrido(3,4-d)pyridazine-1,4(2H,3H)dione - SOD Superoxide dismutase     

Determination of heterotic groups for tropical Indica hybrid rice germplasm

Key message

Two heterotic groups and four heterotic patterns were identified for IRRI hybrid rice germplasm to develop hybrid rice in the tropics based on SSR molecular data and field trials.

Abstract

Information on heterotic groups and patterns is a fundamental prerequisite for hybrid crop breeding; however, no such clear information is available for tropical hybrid rice breeding after more than 30 years of hybrid rice commercialization. Based on a study of genetic diversity using molecular markers, 18 parents representing hybrid rice populations historically developed at the International Rice Research Institute (IRRI) were selected to form diallel crosses of hybrids and were evaluated in tropical environments. Yield, yield heterosis and combining ability were investigated with the main objectives of (1) evaluating the magnitude of yield heterosis among marker-based parental groups, (2) examining the consistency between marker-based group and heterotic performance of hybrids, and (3) identifying foundational hybrid parents in discrete germplasm pools to provide a reference for tropical indica hybrid rice breeding. Significant differences in yield, yield heterosis and combining ability were detected among parents and among hybrids. On average, the hybrids yielded 14.8 % higher than the parents. Results revealed that inter-group hybrids yielded higher, with higher yield heterosis than intra-group hybrids. Four heterotic patterns within two heterotic groups based on current IRRI B- and R-line germplasm were identified. Parents in two marker-based groups were identified with limited breeding value among current IRRI hybrid rice germplasm because of their lowest contribution to heterotic hybrids. Heterotic hybrids are significantly correlated with high-yielding parents. The efficiency of breeding heterotic hybrids could be enhanced using selected parents within identified marker-based heterotic groups. This information is useful for exploiting those widely distributed IRRI hybrid rice parents.     

Genome‐wide identification and analysis of heterotic loci in three maize hybrids

Heterosis, or hybrid vigour, is a predominant phenomenon in plant genetics, serving as the basis of crop hybrid breeding, but the causative loci and genes underlying heterosis remain unclear in many crops. Here, we present a large‐scale genetic analysis using 5360 offsprings from three elite maize hybrids, which identifies 628 loci underlying 19 yield‐related traits with relatively high mapping resolutions. Heterotic pattern investigations of the 628 loci show that numerous loci, mostly with complete–incomplete dominance (the major one) or overdominance effects (the secondary one) for heterozygous genotypes and nearly equal proportion of advantageous alleles from both parental lines, are the major causes of strong heterosis in these hybrids. Follow‐up studies for 17 heterotic loci in an independent experiment using 2225 F₂ individuals suggest most heterotic effects are roughly stable between environments with a small variation. Candidate gene analysis for one major heterotic locus (ub3) in maize implies that there may exist some common genes contributing to crop heterosis. These results provide a community resource for genetics studies in maize and new implications for heterosis in plants.     

Enhancement of protein precipitate strength and density by low-frequency conditioning

The use of a continuous, low-frequency conditioning process to alter the structure of protein precipitate aggregates is examined. An increase in the density of aggregates is correlated with the levels of fluid acceleration and hence hydrodynamic stress to which the aggregates are exposed during conditioning. A combination of low-frequency conditioning followed by shear break-up (as in the feed zone to a high-speed disk-stack centrifuge) is shown to result in a precipitate suspension of increased particle size at the fine end of the distribution, and having a greater sedimentation velocity. The resistance of large aggregates to shear disruption is increased by low-frequency conditioning.List of Symbols CR conditioning ratio - CRS conditioning ratio after shearing - d m amplitude of displacement - D m particle size - D _c m critical size for centrifuge recovery - f s^–1 frequency of vibration - G s^–1 mean velocity gradient - Q m³/s volumetric throughput - SR shear ratio - t s ageing time Greek Symbols s^–1 mass-average shear rate - K sedimentation shape factor - _a kg/m³ aggregate density - _f kg/m³ fluid density - _s kg/m³ solids density - kg/m³ aggregate-suspension density difference - Ns/m² kinematic viscosity - amplitude of pulse ratio (ref. 23, 9) - s mean residence time - _s solids volume fraction     

Hydrodynamic characteristics of two-phase inverse fluidized bed

Hydrodynamic characteristics of a new mode of liquid-solid fluidization, termed as inverse fluidization in which low density floating particles are fluidized with downward flow of liquid, are experimentally investigated. The experiments are carried out with low density particles (<534 kg/m³) which allow high liquid throughputs in the system. During the operation, three regimes, namely, packed, semi-fluidization and fully fluidization are encountered. Empirical correlations are proposed to predict the pressure drop in each regime. A computational procedure is developed to simulate the variation of pressure drop with liquid velocity.List of Symbols Ar modified Archimedes number, d _p ³ (– _s)g/² - d _p particle diameter, mm - f friction factor (eq. 2) - g acceleration due to gravity, m/s² - H total bed height, m - H _c height of the column, m - H_f height of fluidized bed, m - H₀ height of initial bed, m - H_p height of the packed bed, m - (p) pressure drop across the bed, N/m² - (p) _f pressure drop across fluidized bed section, N/m² - (p) _p pressure drop across the packed bed section, N/m² - (p) _sf total pressure drop in semifluidization regime, N/m² - Re Reynolds number, d _pU ₁/ - Re_m modified Reynolds number, d _pU ₁/(1– _p) - U ₁ superficial liquid velocity, m/s - U_mf minimum fluidization velocity, m/s - U_osf onset fluidization velocity, m/s Greek Letters _f voidage of fluidized bed - _p voidage of packed bed - liquid viscosity, kg/ms - liquid density, kg/m³ - _s particle density, kg/m³     

Sequence homology and recombination between the genomes of morphologically dissimilar bacteriophages LP 52 and theta

Summary A restriction fragment map of Bacillus licheniformis temperate phage LP 52 DNA (molecular weight 38.5×10⁶) was established, using restriction endonucleases BamHI (8 target sites), BglI (10 sites), BglII (13 sites) and EcoRI (22 sites). The map is linear, with well-defined ends, without any signs of circular permutation. The DNA of a related phage, LP 51, produced identical restriction fragments. At least 62% DNA of LP 52 has been found homologous to the DNA of the recently discovered, morphologically quite dissimilar, phage , as demonstrated by hybridization of electrophoretically separated restriction fragments of DNA. Under the same conditions, the DNAs of LP 52 and of the morphologically similar Bacillus subtilis phage 105 did not cross-hybridize. The homologous regions in the genomes of phages LP 52 and have been shown to be colinear. Comparison of the cleavage maps of phages LP 52 and has shown that, within the regions of homology, not a single restriction fragment and few restriction sites have been conserved during divergent evolution. Three major regions of heterology were defined; the longest one, covering the right-hand end of the map (73±2.75% up to 100% LP 52 genome length) appeared to contain genes coding for structural proteins of the virions; a shorter region at the left-hand end of the map (coordinates zero to 10.3±3.3% LP 52 genome length) and a very short central region (coordinates 41.8–43.9%) could be identified, the latter apparently containing a regulatory locus responsible for the heteroimmune behavior of the two phages. Recombinants between phages LP 52 and were isolated. Mapping of recombinant genomes has indicated mutual substitution of allelic pieces of LP 52 and DNAs upon strict conservation of overall genome length.     

Localization of a cruciform cutting endonuclease to yeast mitochondria

We have found a cruciform cutting endonuclease in the yeast, Saccharomyces cerevisiae, which localizes to the mitochondria. This activity apparently is associated with the mitochondrial inner membrane since the activity is not released into solution by osmolysis, in contrast to the matrix enzyme, isocitrate dehydrogenase. The cruciform cutting activity appears to be encoded by CCE1. This gene has been shown to encode one of the major cruciform cutting endonucleases present in a yeast cell. In ccel strains, which lack CCE1 endonuclease activity, the mitochondrial cruciform cutting endonucleolytic activity is also absent. Since CCE1 is allelic to MGT1, a gene required for the highly biased transmission of petite mitochondrial DNA in crosses between ⁺ and hypersuppressive ^– cells, it seems likely that the CCE1 endonuclease functions within mitochondria.     

Can spelt wheat be used as heterotic group for hybrid wheat breeding?

Key message

Spelt wheat is a distinct genetic group to elite bread wheat, but heterosis for yield and protein quality is too low for spelt to be recommended as heterotic group for hybrid breeding in wheat.

Abstract

The feasibility to switch from line to hybrid breeding is currently a hot topic in the wheat community. One limitation seems to be the lack of divergent heterotic groups within wheat adapted to a certain region. Spelt wheat is a hexaploid wheat that can easily be crossed with bread wheat and that forms a divergent genetic group when compared to elite bread wheat. The aim of this study was to investigate the potential of Central European spelt as a heterotic group for Central European bread wheat. We performed two large experimental field studies comprising in total 43 spelt lines, 14 wheat lines, and 273 wheat–spelt hybrids, and determined yield, heading time, plant height, resistance against yellow rust, leaf rust, and powdery mildew, as well as protein content and sedimentation volume. Heterosis of yield was found to be lower than that of hybrids made between elite wheat lines. Moreover, heterosis of the quality trait sedimentation volume was negative. Consequently, spelt wheat does not appear suited to be used as heterotic group in hybrid wheat breeding. Nevertheless, high combining abilities of a few spelt lines with elite bread wheat lines make them interesting resources for pre-breeding in bread wheat. Thereby, the low correlation between line per se performance and combining ability of these spelt lines shows the potential to unravel the breeding value of genetic resources by crossing them to an elite tester.

     

Studies on transfer processes in mixing vessels: suspending of solid particles in liquid by modified Rushton turbine agitators

The modified blade turbines are attractive alternatives to the standard Rushton turbine as they do not require any modification in the electrical engine motor and drive assemblies are simple to manufacture and have a reduced power consumption.The modified blades were obtained through increase in the blade height of the Rushton turbine simultaneously with perforation of the blade surface. The field surface of the modified blade is equal to the blade surface of the standard Rushton turbine.In this study the modified blade turbine with the surface fraction of the perforations equal to 0.353 is used.The complete suspension speed and the power dissipation in transition and turbulent regimes using standard and modified Rushton turbine agitators positioned singly or doubly on same shaft, in five solid-liquid systems were investigated.The solid particles used have the mean diameter between 15–1000 m.The modified blade turbine, noted as TP3, was found to be more efficient than the standard turbine in complete and homogeneous suspension.List of Symbols A distance between turbine and the vessel bottom (m) - c dimensionless constant (-) - d agitator diameter (m) - d _p surface-to-volume mean diameter of the particle (m) - D vessel diameter (m) - (H _L )₁ suspension height for one turbine immersed (m) - (H _L )₂ suspension height for two turbines immersed (m) - K consistency index (Pa s ⁿ ) - l _k eddy-size characteristic (m) - N flow behaviour index (-) - N _p number of blades of the mixing system (-) - N agitator speed (s^–1) - N _js agitator speed that just causes complete suspension (s^–1) - Ne P_L/_LN³d⁵ power number in liquid system (-) - (Ne) _g P_g/_spN³d⁵ power number in solid-liquid system (-) - P _L power consumption in liquid system (W) - P _s power consumption in solid-liquid system (W) - r coefficient of correlation (-) - R distance between turbines (m) - Re _spNd²/ _a Reynolds number (-) - S suspension parameter in Zwietering equation (2) (-) - S _C full surface of the blade (m²) - S _G surface of the perforations applied on the blade (m²) - S _G /S _C surface fraction of the perforations (-) - X particle concentration (g/l) - w baffle width (m) - _js specific power input per mass at the complete suspension state (W/kg) - _a apparent viscosity under mixing conditions (Pa s) - _L kinematic viscosity of the liquid (m²/s) - _L density of liquid (Kg/m³) - _s density of solid (Kg/m³) - _sp density of suspension (Kg/m³)     

A possible heterotic threshold in the potato and its implications for breeding

Summary Complex hybrids containing genomes from three different Solanum tuberosum Groups were synthesized (3-way hybrids), utilizing 2n gametes in 4x–2x crosses. Ten such families were compared to nine analogous two-Group (2-way) hybrid families and nine (1-way) families representing conventional Gp. Tuberosum breeding materials. The three types of crosses, representing three descending levels of heterozygosity, were placed in four field trials.The 3-way hybrids were never significantly superior to the 2-way hybrids for vigor, yield, or tuber type. When yields were adjusted for maturity differences, the 3-way hybrids tended to be inferior to the 2-way hybrids for yield. This suggests that there may be a heterotic threshold in the cultivated potato, beyond which point more heterozygosity does not result in greater vigor or more yield.While the 2-way and 3-way hybrids did not significantly differ from each other, they both dramatically surpassed the conventional 1-way crosses for vigor and yield (42%). The evidence of a possible heterotic threshold indicates that more sophisticated methods such as cell fusion and bilateral sexual polyploidization may not be necessary to exploit the full potential of the hybrid approach in the potato. A simple and direct 2-way hybridization approach may be optimal, or at least would seem comparable with other hybrid approaches, and is a technology ready for immediate and widespread implementation.     

Role of mitochondria in ethanol tolerance of Saccharomyces cerevisiae

The presence of active mitochondria and oxidative metabolism is shown to be essential to maintain low inhibition levels by ethanol of the growth rate (), fermentation rate (v) or respiration rate () of Saccharomyces cerevisiae wild type strain S288C. Cells which have respiratory metabolism show K _i (ethanol inhibition constant) values for , v and , higher (K _i>1 M) than those of petite mutants or grande strains grown in anaerobiosis (K _i=0.7 M). In addition, the relationship between or v and ethanol concentration is linear in cells with respiratory metabolism and exponential in cells lacking respiration. When functional mitochondria are transferred to petite mutants, the resulting strain shows K _i values similar to those of the grande strain and the inhibition of and v by increasing ethanol concentrations becomes linear.     

Application of fuzzy multiobjective optimization for self-sucking impellers in a bioreactor

For three types of self-sucking impellers (fourand six-pipe and disk impellers) mixing power, initial point, amount of gas leaving the impeller and mass transfer coefficient were determined experimentally. Investigations were performed for two systems: water and biomass solution.From the point of view of a minimum mixing power and maximum mass transfer coefficient the best impeller has been chosen. Fuzzy multiobjective optimization for determination of optimum operating conditions is proposed.List of Symbols c concentration of oxygen - D tank diameter - d impeller diameter - g acceleration of gravity - H height of liquid in the tank - H height of liquid above impeller, H=H-y - k consistency coefficient - k _L a volumetric mass transfer coefficient - N rotational speed of impeller - n flow behaviour index - P mixing power for pure liquid - P _G mixing power for aerated liquid - V _G volumetric air flow rate - y distance of impeller from the tank bottom - v _a apparent kinematic viscosity of liquid - density of liquid - time - gas hold-up - Eu=P/N ³ d ⁵ or Eu_G=P _G /N ³ d ⁵ Euler Number for non-gassed or aerated liquid - Fr=N ² d/g Froude Number - Fr^*=N ² d ² /g(H -y) modified Froude Number - K_G=V _G /N d ³ gas flow number - Re=N d ² /v _a Reynolds Number - Sh=k _K a/(g ² /v _a )^1/3 Sherwood Number     

Comparison of three granular support materials for anaerobic fluidized bed systems

Summary Three different materials, kaolin, pozzolana and biolite (a material used in a commercial anaerobic fluidized bed treatment process) when tested as supports for an anaerobic fluidized bed system had similar physical and fluidization properties but behaved differently towards the biomass hold-up. However, all three systems attained similar removal efficiency rates.Nomenclature U Fluidization velocity (m/s) - U₁ Terminal fluidization velocity (m/s) - g Local acceleration due to gravity (m/s²) - _s Solid density (kg/m³) - _f Fluid density (kg/m³) - P Pressure drop (Pa) - HRT Hydraulic retention time (days) - H_mf Height of bed at minimum fluidization (m) - H Height of bed (m) - C_d Drag coefficient (dimensionless) - W Mass of solids in bed (kg) - dp Particle diameter (m) - A Cross-sectional area of column (m²) - h column height (m) - Rc_t Terminal Reynolds no. - Voidagc (fractional free volume, dimensionless) - _mf Voidage (fractional free volume) at minimum of fluidization (dimensionless)     

Vascular dynamics

A study, using the four-electrode impedance plethysmograph system, was completed to evaluate simultaneous variations in conduction of upper and lower body segments relative to displacement of blood volume during change in body position. Measurements of cardiac output were compared with simultaneous results by dye dilution methods as a means of assessing the use of impedance techniques to determine cardiac output during tilt table studies. Two groups, 48 healthy private pilots and 22 patients with diabetes mellitus, were tested and the results were compared.Control and test heart rate values were higher in the afternoon than in the morning for the same healthy subjects, and the blood pressure and heart rate changes paralleled the variations in stroke volume and calf blood pulse changes. The results in the patients with diabetes differed markedly in terms of the magnitude of the cardiovascular changes and indicated the value of the tilt table in assessing fatigue in the circulatory system as a result of metabolic disturbance. The change from horizontal to 65 degree head up position in the patients with diabetes showed a marked fall in thoracic stroke and conductive volume in contrast to the minimal decrease observed in healthy subjects.Symbols resistivity, ohm cm - L length or distance between detecting electrodesE ₁-E ₂, cm - E voltage, volts - I current, amps - R ₀ segmental resistance between detecting electrodesE ₁-E ₂, ohms - V ₀ segmental volume equivalent to (L ²/R ₀), ml - V change in volume, ml - R change in resistance, ohms Terms Impedance plethysmography Measurement of change in volume due to variation in electrical resistance of a segment to a 50 or 120 kHz signal. The impedance at these frequencies is primarily resistive - Four electrodes Two electrodes for introduction of the reference signal to the examined segment and two electrodes for detecting variation in conduction of the signal - Conduction The reciprocal of resistance measured in mohs. - Conductive volume The volume defined byV ₀=(L ²/R ₀) containing electrolytes including whole blood and plasma This project was supported by Contract NAS4-1321, NASA Flight Research Center, Edwards, California, U.S.A.     

Polyclonal IgE increase after H9CI2 injections in BN and LEW rats: A genetic analysis

An autoimmune disease and a dramatic increase in total serum IgE concentration are observed in BN rats that are chronically injected with HgCl₂. In contrast, LEW rats do not develop the characteristic glomerulonephritis and are very low IgE responders. In this study, we examined the genetic control of total serum IgE increase after HgCl₂ injection in F₁ and F₂ hybrids, in both backcrosses between LEW and BN rats, and in LEW.1N congenic rats. Genetic analysis was performed using peak IgE concentrations expressed as log g/ml. A high IgE phenotype was found to be dominant. Eighty-five percent of F₂ variance was due to genetic factors (VG) while only 15% of this variance was caused by environmental factors (VE). From observations in F₂ hybrids and backcrosses, estimations of additive variance (VA) and dominance variance (VD) were made following three different methods. Genetic control by about four loci is demonstrated. One of these genes is RT1-linked. This gene contributes to 25% of the phenotypic difference observed between BN and LEW rats. No correlation was found between the peak total IgE level and autoimmune disease based on IgG deposition in spleen and/or kidney.     

The mh gene causing double-muscling in cattle maps to bovine Chromosome 2

While the hereditary nature of the double-muscling phenotype (a generalized muscular hypertrophy documented in several cattle breeds) is well established, its precise segregation mode has remained controversial. Both monogenic models (autosomal dominant or recessive) and oligogenic models have been proposed. Using a panel of 213 bovine microsatellite markers, and an experimental pedigree obtained by backcrossing double-muscled (Belgian Blue)xconventional (Friesian) F₁ dams to double-muscled sire, we have mapped a locus on bovine Chromosome (Chr) 2 that accounts for all the phenotypic variance in the backcross generation. This locus, referred to as mh (muscular hypertrophy), has been positioned with respect to a map composed of seven Chr 2-specific microsatellites, at 2 cM from the closest marker. This result confirms the validity in the Belgian Blue population of the monogenic model involving an autosomal mh locus, characterized by a wild-type + and a recessive mh allele, causing the double-muscling phenotype in the homozygous condition. The linkage relationship between the mh locus and the Chr 2 markers was confirmed in three informative pedigrees collected from the general Belgian Blue Cattle population, reinforcing the notion of genetic homogeneity of the double-muscling trait in this breed. This work paves the way towards marker-assisted selection for or against the double-muscling trait, and towards positional cloning of the corresponding gene.     

Structural comparison of the genes of two HLA-DR supertypic groups: The loci encoding DRw52 and DRw53 are not truly allelic

The organization and sequence of the HLA-DR chain genes are compared in the two supertypic groups, DRw52 and DRw53, which together account for more than 80% of HLA-DR alleles. From the structural data, we conclude that these two groups represent distinct lineages which have followed different patterns of evolution. The fine structure of the chain locus encoding the DRw53 specificity corresponds most closely to the DR II pseudogene in the DRw52 haplotypes. Concomitantly, the DR I locus in DRw53 haplotypes is more closely related to both of the two expressed DR loci of theDRw5 haplotypes (DR I and DR III). These two loci are the result of a recent duplication. This leads to the proposal that both expressed DR chain genes in the DRw52 haplotypes (DR I and DR III) are derived from a single precursor locus, while the two loci expressed in the DRw53 haplotypes are derived from distinct ancestral loci. The genes encoding DRw52 and DRw53 are therefore not true alleles of the same original locus. A scheme is proposed that accounts for the evolution of DR specificities within the DRw52 and DRw53 groups of haplotypes. It is evident that the differentHLA-DR alleles are not structurally equidistant and that one must take into consideration different degrees of heterozygosity or mismatch among the DR alleles.