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.     

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.     

The modulation of membrane fluidity by hydrogenation processes. III. The hydrogenation of biomembranes of spinach chloroplasts and a study of the effect of this on photosynthetic electron transport

A method is reported for the in situ modification of the lipids of isolated spinach chloroplast membranes. The technique is based on a direct hydrogenation of the lipid double bonds in the presence of the catalyst, chlorotris(triphenylphosphine)rhodium (I). The pattern of hydrogenation achieved suggests that the catalyst distributes amongst all of the membranes. The polyunsaturated lipids within the membranes are hydrogenated at a faster rate and at an earlier stage than are the monoenoic lipids.Whilst addition of the catalyst to the chloroplast causes an initial 10–20% decrease in Hill activity, saturation of up to 40% of the double bonds present can be accomplished without causing further significant alterations in photosynthetic electron transport processes or marked morphological changes of the chloroplast structure as observed in the electron microscope.     

Protein-lipid interaction. Biophysical studies of (Ca2+ + Mg2+)-ATPase reconstituted systems

Differential scanning calorimetry, fluorescence spectroscopy and freeze-fracture electron microscopy have been applied to a study of the reconstituted Ca2+-ATPase proteins from sarcoplasmic reticulum when they are incorporated into pure lipid/water systems. The results obtained with these techniques have been used to examine the effects of this intrinsic protein upon the surrounding lipid at temperatures above and below the main lipid solid-fluid phase transition temperature (Tc). 1. Above this Tc value, the freeze-fracture data show that the proteins are randomly distributed within the plane of the bilayer. The fluorescence data show that as the protein content in the bilayer increases, so does the 'microviscosity'. 2. Below Tc the proteins occur in high protein to lipid patches, separate from the remaining crystalline lipid. The fluorescence data indicate that at these temperatures the presence of the protein causes a decrease in microviscosity, whilst the calorimetric data indicate a decrease in enthalpy of the main lipid transition. 3. A premelting of the high protein to lipid patches formed by phase separation within the lipid bilayers is indicated by the calorimetric and fluorescence data. This observation is used to rationalise the 'anomalous' properties of the dipalmitoyl phosphatidylcholine-ATPase of exhibiting activity at temperatures well below the lipid phase transition at 41 degrees C.     

Protein-lipid interactions and differential scanning calorimetric studies of bacteriorhodopsin reconstituted lipid-water systems

Bacteriorhodopsin has been reconstituted at various molar concentrations into liposomes of dimyristoyl- and also of dipalmitoylphosphatidylcholine. Differential scanning calorimetry indicates that as the protein concentration within the lipid bilayer increases, the cooperativity of the lipid phase transition is reduced, i.e. the transition is broadened, while the midpoint transition temperature remains virtually unchanged. Freeze-fracture electron microscopy of our preparation shows, in agreement with previous data from other laboratories, that extensive protein aggregation occurs when the liposome is cooled below the T_c transition temperature of the lipid. Laser flash photolysis measurements of protein rotation of the bacteriorhodopsin show, especially in the case of protein-rich recombinants, that protein aggregates exist even above T_c. The perturbation caused by the presence of bacteriorhodopsin in the lipid bilayer is similar to that produced by other intrinsic proteins. The difficulty of correlating the observed calorimetric enthalpy data with a simple concept of a ‘boundary lipid layer’ based upon consideration of a single isolated protein is discussed in view of the occurrence of protein aggregates both above and below T_c. It is concluded that the reduction of enthalpy is related to the number of lipids which solvate the protein aggregates within the protein-lipid patches and are thereby removed from the cooperative melting and enthalpy of the remaining regions of pure lipid.     

Protein rotation, enzyme activity and photooxidation of SH groups in sarcoplasmic reticulum Ca2+-ATPase

The binding of probe molecules such as fluorescein isothiocyanate, eosin isothiocyanate and erythrosin isothiocyanate to the Ca2+-ATPase of sarcoplasmic reticulum followed by illumination of the labelled protein causes substantial reductions of ATPase activity over a 1-h period. The degree of light-sensitivity induced by these probes is related to the triplet yield of these probe molecules. Consistent with this, the greatest effect is seen with erythrosin isothiocyanate and the least effect with fluorescein isothiocyanate. These reductions of ATPase activity associated with illumination are also associated with an aggregation of the protein molecules. This is indicated by laser flash photolysis measurements and also by polyacrylamide gel electrophoresis. A reduction in the number of thiol groups present on the ATPase molecule parallels the reduction of enzyme activity and changes in the protein mobility. The results are discussed in relation to the use of these probe molecules to study biological systems and also in terms of oxidative processes which may affect protein function in vivo.     

A study on the minimum number of loci required for genetic evaluation using a finite locus model

For a finite locus model, Markov chain Monte Carlo (MCMC) methods can be used to estimate the conditional mean of genotypic values given phenotypes, which is also known as the best predictor (BP). When computationally feasible, this type of genetic prediction provides an elegant solution to the problem of genetic evaluation under non-additive inheritance, especially for crossbred data. Successful application of MCMC methods for genetic evaluation using finite locus models depends, among other factors, on the number of loci assumed in the model. The effect of the assumed number of loci on evaluations obtained by BP was investigated using data simulated with about 100 loci. For several small pedigrees, genetic evaluations obtained by best linear prediction (BLP) were compared to genetic evaluations obtained by BP. For BLP evaluation, used here as the standard of comparison, only the first and second moments of the joint distribution of the genotypic and phenotypic values must be known. These moments were calculated from the gene frequencies and genotypic effects used in the simulation model. BP evaluation requires the complete distribution to be known. For each model used for BP evaluation, the gene frequencies and genotypic effects, which completely specify the required distribution, were derived such that the genotypic mean, the additive variance, and the dominance variance were the same as in the simulation model. For lowly heritable traits, evaluations obtained by BP under models with up to three loci closely matched the evaluations obtained by BLP for both purebred and crossbred data. For highly heritable traits, models with up to six loci were needed to match the evaluations obtained by BLP.