Optimizing purebred selection for crossbred performance using QTL with different degrees of dominance

A method was developed to optimize simultaneous selection for a quantitative trait with a known QTL within a male and a female line to maximize crossbred performance from a two-way cross. Strategies to maximize cumulative discounted response in crossbred performance over ten generations were derived by optimizing weights in an index of a QTL and phenotype. Strategies were compared to selection on purebred phenotype. Extra responses were limited for QTL with additive and partial dominance effects, but substantial for QTL with over-dominance, for which optimal QTL selection resulted in differential selection in male and female lines to increase the frequency of heterozygotes and polygenic responses. For over-dominant QTL, maximization of crossbred performance one generation at a time resulted in similar responses as optimization across all generations and simultaneous optimal selection in a male and female line resulted in greater response than optimal selection within a single line without crossbreeding. Results show that strategic use of information on over-dominant QTL can enhance crossbred performance without crossbred testing.     

Periodicity of bud bursting in willow (Salix viminalis) as affected by growth regulators

Saunders, P. F. and Barros, R. S. 1987. Periodicity of bud bursting in willow ( Salix viminalis ) as affected by growth regulators.
Lateral vegetative buds of willow ( Salix viminalis L.) were only innately dormant for 3–5 weeks in October; during this time their apices were correlatively inhibited by the bud leaflets. Exogenous gibberellins stimulated the opening of cultured buds when the plants were dormant or entering dormancy. As dormancy was being released, however, cultured buds became more responsive to exogenous cytokinins. Thus the demand for gibberellins and cytokinins for bud opening seemed to be sequential rather than simultaneous. Dormant buds cultured in the presence of abscisic acid remained unopened, but they opened after a chilling treatment. Subsequent growth of such buds as measured by dry matter accumulation, was observed only if a cytokinin was added to the medium.     

Cloning and expression in Escherichia coli of a cellulase gene from Ruminococcus flavefaciens.

An endoglucanase gene of Ruminococcus flavefaciens FD1 was cloned on the vector pEcoR251 to form the recombinant plasmid pMEB200. The cloned endoglucanase gene showed carboxymethylcellulase enzyme activity but no degradation of Avicel (FMC Corp., Philadelphia, Pa.) or filter paper. Carboxymethylcellulase activity was found during the late-exponential-growth phase and accumulated in the periplasmic fraction. Enzyme production was not subject to catabolite repression by glucose.     

Production of ethanol by immobilized Saccharomyces bayanus in an extractive fermentation system

An extractive fermentation system using immobilized yeast cells was developed to study the ethanol production at high sugar concentrations. Organic acids were used as extracting solvents of ethanol and their toxicity was tested in free and k-carrageenan entrapped cell preparations. Immobilization seems to protect cells against solvent toxicity, when long-chain organic acids, e.g., oleic acid, were used, probably due to steric and diffusional limitations, the free cells not being viable at high oleic acid concentrations. The entrapped cells also present a higher metabolic activity than their free counterparts at high glucose concentrations. A solution of 300 g/L of glucose was totally fermented by the immobilized yeast cells, which when free cannot normally convert more than 200 g/L. In situ recovery of ethanol by oleic acid in a batch immobilized cell system led to higher ethanol productivities and to the fermentation of 400 g/L, when an oleic acid/medium ratio of 5 was used.     

A complex balanced chromosomal rearrangement in repeated abortions

Summary A double balanced reciprocal translocation involving four chromosomes, t(1;19;6;14) (1p11; 19p11; 6q25; 14q21), was found in the phenotypically normal husband in a couple referred because of repeated abortions. Reciprocal translocations, t(6;14), had been transmitted by his mother, his father being apparently homozygous for a translocation comprising pairs 1 and 19-t(1;19)(1;19). The genetic consequences of this complex chromosomal rearrangement are analyzed.     

Mutations in cell division cycle genes CDC36 and CDC39 activate the Saccharomyces cerevisiae mating pheromone response pathway.

Conditional mutations in the genes CDC36 and CDC39 cause arrest in the G1 phase of the Saccharomyces cerevisiae cell cycle at the restrictive temperature. We present evidence that this arrest is a consequence of a mutational activation of the mating pheromone response. cdc36 and cdc39 mutants expressed pheromone-inducible genes in the absence of pheromone and conjugated in the absence of a mating pheromone receptor. On the other hand, cells lacking the G beta subunit or overproducing the G alpha subunit of the transducing G protein that couples the receptor to the pheromone response pathway prevented constitutive activation of the pathway in cdc36 and cdc39 mutants. These epistasis relationships imply that the CDC36 and CDC39 gene products act at the level of the transducing G protein. The CDC36 and CDC39 gene products have a role in cellular processes other than the mating pheromone response. A mating-type heterozygous diploid cell, homozygous for either the cdc36 or cdc39 mutation, does not exhibit the G1 arrest phenotype but arrests asynchronously with respect to the cell cycle. A similar asynchronous arrest was observed in cdc36 and cdc39 cells where the pheromone response pathway had been inactivated by mutations in the transducing G protein. Furthermore, cdc36 and cdc39 mutants, when grown on carbon catabolite-derepressing medium, did not arrest in G1 and did not induce pheromone-specific genes at the restrictive temperature.     

Effect of postnatal development on calcium currents and slow charge movement in mammalian skeletal muscle

Single- (whole-cell patch) and two-electrode voltage-clamp techniques were used to measure transient (Ifast) and sustained (Islow) calcium currents, linear capacitance, and slow, voltage-dependent charge movements in freshly dissociated fibers of the flexor digitorum brevis (FDB) muscle of rats of various postnatal ages. Peak Ifast was largest in FDB fibers of neonatal (1-5 d) rats, having a magnitude in 10 mM external Ca of 1.4 +/- 0.9 pA/pF (mean +/- SD; current normalized by linear fiber capacitance). Peak Ifast was smaller in FDB fibers of older animals, and by approximately 3 wk postnatal, it was so small as to be unmeasurable. By contrast, the magnitudes of Islow and charge movement increased substantially during postnatal development. Peak Islow was 3.6 +/- 2.5 pA/pF in FDB fibers of 1-5-d rats and increased to 16.4 +/- 6.5 pA/pF in 45-50-d-old rats; for these same two age groups, Qmax, the total mobile charge measurable as charge movement, was 6.0 +/- 1.7 and 23.8 +/- 4.0 nC/microF, respectively. As both Islow and charge movement are thought to arise in the transverse-tubular system, linear capacitance normalized by the area of fiber surface was determined as an indirect measure of the membrane area of the t-system relative to that of the fiber surface. This parameter increased from 1.5 +/- 0.2 microF/cm2 in 2-d fibers to 2.9 +/- 0.4 microF/cm2 in 44-d fibers. The increases in peak Islow, Qmax, and normalized linear capacitance all had similar time courses. Although the function of Islow is unknown, the substantial postnatal increase in its magnitude suggests that it plays an important role in the physiology of skeletal muscle.     

A Study of Magnetic Properties of Magnetotactic Bacteria

The first direct measurements of magnetic properties of magnetotactic bacteria from natural samples are presented. Measurements were made at 4.2 K, using a Superconducting Quantum Interfering Device (SQUID) magnetometer. From the magnetization results an anisotropy is obtained that is typical of magnetized ferro- or ferri-magnetic materials. The average magnetic moment of the bacteria determined from the results is in good agreement with the estimated moment from electron microscopy.     

Na+/H+ exchange is present in basolateral membranes from rabbit small intestine

Fluorescence quenching of the pH gradient sensitive dye acridine orange and that of the membrane potential sensitive dye Di-S-C3(5) have been studied in purified basolateral membrane vesicles obtained from rabbit small intestine. Basolateral membranes contain an electroneutral, carrier mediated, Na+/H+ exchange activity. They also appear to contain an electrogenic pathway for H+ movement. Based on the comparison of acridine orange fluorescence quenching in the presence of an outwardly directed Na+ gradient and in the presence of known K+ diffusion gradients it can be estimated that at least 50% of the observed proton fluxes are due to the activity of the exchanger. Acridine orange fluorescence recovery measurements have been used to assess the kinetic properties of the exchanger.