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.     

Variability in response to UV-B among species and strains of Metarhizium isolated from sites at latitudes from 61 degrees N to 54 degrees S.

The effects of irradiances of 920 and 1200 mW m(-2) (biologically effective weighted irradiance) were examined in 2 Metarhizium album strains, 26 M. anisopliae strains, 1 M. flavoviride strain, and 1 M. taii strain isolated from sites located at latitudes from 61 degrees N to 54 degrees S. Conidia were exposed to UV-B from 1 to 6 h and subsequently examined for relative percentage culturability. Total dosage received at the end of the exposure periods ranged from 3.3 to 19.9 kJ m(-2) for the lower irradiance and from 4.3 to 25.9 kJ m(-2) for the higher irradiance. Both the irradiance values and the doses are environmentally realistic and can be observed even in temperate regions. The relationships between latitude of origin and UV-B tolerance were compared for the two levels of irradiance for the data from 1 and 2 h exposure. Exposure to both irradiances drastically reduced the relative percentage culturability of all strains. Tolerance to UV-B varied widely among strains and high variation was observed for both irradiances after all periods of exposure. After 1 h of exposure, a difference between the two irradiance levels was detectable, and this difference was magnified at longer irradiations. A significant quadratic relationship of decreasing UV-B tolerance with increasing latitude was observed after exposure of 1 and 2 h. The shape of the relationship did not differ for the two levels of irradiance. Also, we studied the effect of 1200 mW m(-2) irradiance on conidial germination time in 1 M. album strain, 7 M. anisopliae strains, and 1 M. taii strain. Exposure to UV-B delayed the germination of surviving conidia of all strains. In general, the delay in germination was directly proportional to the dose.     

β-thalassemia mutations in the Portuguese population

Summary In this study we have carried out haplotype analysis on the -globin gene cluster and characterized the -thalassemia mutation by oligonucleotide hybridization in 14 patients with thalassemia major and 5 with sickle cell/-thalassemia originating from southern Portugal. We found that three mutations, namely the °-39, ° IVS-1 nt 1 and ⁺ IVS-1 nt 110 are prevalent accounting for 53%, 32% and 10% of the -thalassemia chromosomes respectively. In general each mutation was associated with a specific chromosomal haplotype; the ° mutation, however, was linked to three different haplotypes. These results indicate that three oligo-probes complementary to the most common mutations allow prenatal diagnosis by oligonucleotide analysis in 96% of the couples at risk of having offspring with thalassemia major in southern Portugal.     

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.     

Molecular deletion patterns in Duchenne and Becker type muscular dystrophy

Summary DNA from 80 Duchenne (DMD) and 15 Becker (BMD) index patients was analyzed with 12 genomic probes and the total cDNA. Deletions were detected in 24 DMD (30%) and 10 BMD patients (67%) by genomic probes alone, mostly p20, pXJ, and/or pERT87. All deletions were confirmed by cDNA probes, and an additional 29 DMD deletions were detected, resulting in a total of 63/95 deletions (66%). The majority of the deletions are localized between kb 6.7 and 9.7 of the cDNA; a smaller group, between kb 0.5 and 3.5. Of the deletions, 90% are detected by the three cDNA probes 1–2a, 7, and 8. This can be applied to strategies for carrier detection and prenatal diagnosis. The order of 13 exon-containing HindIII fragments in the region between probes 7 and 9–10, where most of the deletions are found, could be defined. The deletion patterns in DMD and BMD patients are different and well in accordance with the “reading frame theory” of Monaco and coworkers. Thus our findings indicate that a DMD or BMD phenotype may be predicted according to the breakpoint position and the number of deleted exons.     

Effects of pH and ionic strength on the structure of collagen fibrils

The roles of pH and ionic strength on the structure and stability of collagen fibrils have been investigated by means of x-ray and neutron diffraction techniques. High-angle x-ray diffraction shows that a salt concentration of 0.5M KCl is sufficient to reduce the osmotic swelling and related disordering in the pH range 1–3. The relative intensities of the low-angle meridional x-ray and neutron diffraction Bragg reflections vary with pH. Difference Fourier syntheses between pH 7 and 1.6 data indicate, for both x-ray and neutron diffraction, a reduced scattering contribution from the telopeptides at low pH. Lyotropic relaxation is a crucial step in the appearance at low pH of a doubling of the 668-Å axial periodicity (D) of collagen fibrils. These results suggest that electrostatic interactions are essential for the structural stability of the telopeptide regions and of the 1D and 3D intermolecular staggers between collagen molecules.