On the fixation of genes of large effects due to continued truncation selection in small populations of polygenic systems with linkage

Summary The proportion of fixed loci for desirable genes and the time required for fixation is studied in simulated diploid populations, which have initially aHardy-Weinberg structure. A symmetric ten-locus system of additive or dominant genes is simulated with linkages between adjacent loci varying as .005, .05, or .5. A constant degree of upper truncation selection within a population is considered over the generations. In different populations the intensity of truncation is varied asN/N,N/N+2,N/N+4, ..., whereN is the parental population size, specified as 2,4,8 or 16. The selection differential in initial generation, , thereby varies from zero to more than two standard deviations in some cases. The initial mean gene frequency,p, simulated in an initial population is .1 or .5.It is pointed out that when selective advantage of a gene is large and is changing with gene frequency, diffusion approximations assuming constant selective advantage, gives higher values for proportion of fixed genes in the case ofp equal to .1 and lower values forp equal to .5. With parental population size of 16 or less, a relation withN alone does not give the proportion of fixed genes. Higher order terms ofN appear to be involved in the relation. For the sameN , the proportion is much higher for lowN.The depressing effect of low recombinations between loci is of different magnitude for differentN andp for a givenN . The increase in the proportion of fixed genes due to increasingN is not as large when is low. High intensity of selection offsets considerably the effects of population size and linkage when gene effects are large. It appears that with increased inbreeding and selection intensity, almost all the genes of large effects and at intermediate frequencies can be rapidly fixed regardless of linkage.Linkage has been shown to cause faster fixation of genes in the absence of selection. With selection, linkage tends to delay fixation. But in the case of very low recombinations, there appears to be a level of population size and selection intensity, below which there is more rapid fixation because of linkage. Selection for dominant genes in the case of very close linkage, delays fixation for a number of generations and this delay results in reducing the depressing effect of linkage.

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Zusammenfassung Der Anteil fixierter Loci für erwünschte Gene und die für die Fixierung erforderliche Zeit werden in einer simulierten diploiden Population untersucht, wobei eine ursprünglicheHardy-Weinberg-Struktur angenommen wird. Es wird ein symmetrisches 10-Locus-System von additiven oder dominanten Genen mit Koppelung zwischen benachbarten Loci, die von 0,005 über 0,05 bis zu 0,5 variiert wird, simuliert. Hierbei wird ein konstantes Ausmaß von trunkierender (stutzender) Selektion für die Obergrenze der Verteilung in der Population betrachtet. In verschiedenen Populationen wird die Intensität der Verteilungsstutzung variiert in der folgenden FormN/N,N/N+2,N/N+4, ..., wobeiN die elterliche Populationsgröße ist, die mit 2,4,8 oder 16 spezifiziert wird. Das Selektionsdifferential der Ursprungsgeneration,i, variiert hierbei in einigen Fällen von 0 bis auf mehr als 2 Standardabweichungen. Die ursprüngliche mittlege Genfrequenz,p, die in einer Ausgangspopulation simuliert wird, ist 0,1 oder 0,5.Es wird gezeigt, daß, im Vergleich zu großem selektivem Vorteil eines Gens und frequenzabhängiger Änderung des Selektionskoeffizienten, Diffusionsnäherungen, die konstante selektive Vorteile voraussetzen, höhere Werte für den Anteil fixierter Gene im Fallp=0,1 und niedrigere Werte fürp=0,5 ergeben. Mit einer elterlichen Population der Größe 16 oder kleiner ergibt die BeziehungNi allein nicht den Anteil fixierter Gene, da Termini höherer Ordnung vonNi in die Bezichung einbezogen sind. Bei gleichemNi ist der Anteil bei kleinemN viel höher. Der reduzierende Effekt einer niederen Rekombinationsrate zwischen den Loci ist von unterschiedlicher Größenordnung bei verschiedenemN und bei einem gegebenenNi. Der Zuwachs im Anteil fixierter Gene infolge eines wachsendenN ist nicht so groß, wennp niedrig ist. Eine hohe Intensität der Selektion gleicht die Wirkungen der Populationsgröße und Koppelung erheblich aus, wenn die Genwirkungen groß sind. Es zeigt sich, daß praktisch alle Gene mit großer Wirkung und intermediärer Frequenz unabhängig von der Koppelung schnell fixiert werden können, wenn eine zunehmende Inzucht und Selektionsintensität vorliegt.Koppelung hat sich als eine Ursache für eine schnellere Fixierung von Genen in der Abwesenheit von Selektion erwiesen. Mit Selektion tendiert Kopplung dazu, die Fixierung zu verzögern. Es zeigt sich jedoch im Falle einer sehr niederen Rekombinationsrate, daß es für die Populationsgröße und Selektionsintensität einen Schwellenwert zu geben scheint, unterhalb dessen eine schnellere Fixierung als Folge der Koppelung auftritt. Eine Selektion auf dominante Gene verzögert im Fall der sehr engen Koppelung die Fixierung für eine Anzahl von Generationen und diese Verzögerung führt dazu, daß der verlangsamende Effekt der Koppelung reduziert wird.

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On leave from West Pakistan Agricultural University, Lyallpur.

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Journal paper No. 5870, Iowa Agriculture and Home Economics Experiment Station, Ames, supported by National Institute of Health Grant No. GM 13827.     

Effect of lactic acid on growth and butanediol production byKlebsiella oxytoca

Summary Production of 2,3-butanediol byKlebsiella oxytoca was enhanced in the presence of low levels (<8 g/l) of added sodium lactate. Cell growth was inhibited, however, and essentially stopped above 15 g/l added lactate. Levels of by-products (acetic acid and ethanol) were also higher. With 3 g/l lactate and an initial glucose level of 98 g/l, butanediol concentration and productivity increased 164% with 98% utilization of glucose. With high glucose concentration (219 g/l), addition of 2.64 g/l lactate after the growth phase resulted in 81 g/l butanediol, with a productivity of 0.65 g/l/h and 71% glucose utilization.     

The importance of mast cells for the neutrophil influx in immune complex-induced peritonitis in mice

The role of mast cells in polymorphonuclear leukocyte (PMN) influx in Ag-antibody complex-induced peritonitis was evaluated in mast cell-deficient WBB6F1-W/Wv (W/Wv) mice and their normal littermates, WBB6F1-+/+ (+/+). Peritoneal cell influx was evaluated after i.p. injection of preformed immune complexes. The first significant elevation in the PMN count over PBS-treated controls in +/+ mice was observed 2 h after stimulation. During the period of maximum leukocyte concentrations (6 to 10 h), the increase in total cell count was 5-fold and in PMN 25-fold. In W/Wv mice the PMN influx started 2 h later than in the +/+ mice, and the maximum response (8 to 10 h) was only 50% of that in controls. Reconstitution of mast cells in W/Wv mice for 2 wk or more restored the PMN response to immune complexes. Mast cell release due to AG-antibody complexes was evaluated by measuring fluorescence intensity after berberine sulfate staining for heparin in mast cells from unstimulated as well as stimulated +/+ mice. There was a significant decrease in fluorescence intensity as early as 15 min after stimulation. By 30 min the fluorescence intensity had declined by 65%. This indicates extensive mast cell release that started before PMN mobilization. These experiments demonstrate that mast cells make a significant contribution to immune complex-induced inflammation.     

Evidence for a plasmid conferring salt-tolerance in the plant-root associated,diazotrophKlebsiella sp. NIAB-I

Summary Using analytical and preparative methods, we demonstrated the presence of an indigenous plasmid (pNIAB-I) in a diazotroph,Klebsiella sp. NIAB-I isolated, from the roots of Kallar grass, growing on saline lands in Pakistan. The plasmid is approximately 50 kilobase (kb) in size. Transformation experiments indicated that non-halophilic bacteria such asE. coli K12 strain (MV10) andK. pneumoniae M5AI on acquiring this plasmid become tolerant to high salt (NaCl) and alkaline pH.     

Dietary zinc-methionine enhances mononuclear-phagocytic function in young turkeys

The ability of dietary zinc-methionine (Zn-Met) to enhance mononuclear-phagocytic function againstSalmonella arizona andenteritids was investigated in young turkeys. Feed/gain and body wt gain at 21 d of age were not affected by Zn-Met. The addition of 30 or 45 ppm Zn from Zn-Met to a Zn adequate diet significantly increased cutaneous basophil hypersensitivity to phytohemagglutinin-P. The clearance of intravenously administeredS. enteritidis from blood was not affected by 30 ppm of supplemental Zn from Zn-Met. However, 30 ppm Zn from Zn-Met increased the reduction of intravenously administeredS. arizona from spleen. Percentages of myeloid and mononuclear-phagocytic cells before and afterS. enteritidis infection were not affected by supplemental Zn-Met. Turkeys supplemented with Zn-Met showed enhanced in vitro phagocytosis ofS. enteritidis by Sephadex-elicited abdominal exudate cells. The phagocytosis ofS. arizona was unaffected by Zn-Met.     

Characterization of a high-affinity binding site for a DNA-binding protein from sea urchin embryo mitochondria.

Based on electrophoretic mobility shift assays, DNase I footprinting and modification interference analyses we have identified a sequence-specific DNA-binding protein in blastula stage mitochondria of the sea urchin Strongylocentrotus purpuratus, which interacts with a binding site around the major pause site for DNA replication. This region straddles the boundary of the genes for ATP synthase subunit 6 and cytochrome c oxidase subunit III, and contains also a prominent origin of lagging-strand synthesis. The protein is thermostable, and its natural high-affinity binding site comprises the sequence 5'-AGCCT(N7)AGCAT-3'. Binding studies have demonstrated that two copies of the imperfect repeat, as well as the 7 bp spacing between them, are essential for tight binding. Based on the location of its binding site, we tentatively designate the protein mitochondrial pause-region binding protein (mtPBP) 1.     

Cryopreservation of immature spring wheat zygotic embryos using an abscisic acid pretreatment

Spring wheat (Triticum aestivum L.) zygotic embryos were successfully cryopreserved, without the addition of exogenous cryoprotectants, using only an abscisic acid (ABA) pretreatment. Optimum survival was obtained when embryos were cultured in vitro for 10 days on semisolid Murashige and Skoog (MS) nutrient medium supplemented with 0.5 mg/L (±) ABA prior to cryopreservation. The embryos resumed growth within three days when returned to MS medium devoid of ABA but containing 2mg/L 2,4-dichlorophenoxyacetic acid. The embryogenic calli produced from these embryos exhibited normal plant regeneration on auxin-free media. Changes in dw/fw ratio, as well as the esterified fatty acid and sucrose concentrations correlated positively with the development of tolerance to cryopreservation.NRCC Publication No. 33519     

Metal tolerance in tissue cultures of anthoxanthum odoratum

Tissue cultures were initiated from one non-tolerant (S20) and two zinc and lead tolerant (T92 and T94) clones of Anthoxanthum odoratum. Growth of callus from the non-tolerant clone was reduced by the presence of zinc, lead, copper and nickel, whereas callus from the two tolerant clones showed no reduction of growth in the presence of zinc and lead but growth was reduced by copper and nickel. The specificity of metal tolerance shown by the parental material was maintained in the callus. Tolerant and non-tolerant callus accumulated similar amounts of zinc and lead.     

L-histidine induced changes in adenosine 3':5'-monophosphate levels in rat brain and amounts of apo-, holo-a and holo-b fatty acid synthetases in rat liver.

When fasted rats were fed a chow or fat-free diet supplemented 5% with L-histidine for three days, the brain adenosine 3′:5′-monophosphate (cAMP) level increased. A 50% increase occurred in rats fed a chow diet and 20% increase in rats fed a fat-free diet. Purification of liver fatty acid synthetase and the isolation of liver apo-, holo-$\text{a}$ and holo-$\text{b}$ fatty acid synthetases demonstrated that L-histidine feeding caused changes in the relative amounts of these enzymes. Apo- and holo-$\text{b}$ fatty acid synthetases increased while the holo-$\text{a}$ form simultaneously decreased. This effect was observed in rats fed either chow or fat-free diets supplemented with L-histidine.     

L-histidine-induced suppression of lipogenic enzymes.

Diets supplemented 5% with L-histidine produce hypercholesterolemia and increase cholesterol biosynthesis in rat liver. We now report an $\text{inhibitory}$ effect of L-histidine on lipogenic enzymes in the liver. In this study, L-histidine was added to chow and fat-free diets and fed to rats for 18 days. After two days of fasting, the rats were refed the same diet for three days prior to sacrifice. L-histidine decreased fatty acid synthetase activity by 51% when it was added to the chow diet and by 26% when it was added to the fat-free diet. Isocitrate dehydrogenase activity was not altered significantly in rats fed diets supplemented with L-histidine.