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.     

Cytochrome P450cam-catalyzed oxidation of a hypersensitive radical probe.

trans-1-Phenyl-2-vinylcyclopropane, a hypersensitive radical probe, is oxidized by cytochrome P450cam (CYP101) to a diastereomeric mixture of the corresponding epoxide (81%), (trans-2-phenylcyclopropyl)acetaldehyde (6%), and trans-5-phenyl-2-penten-1,5-diol (13%). trans-5-Phenyl-2-penten-1-ol and (trans-2-phenylcyclopropyl)ethane-1,2-diol are not detectably formed. Authentic standards of all the products have been synthesized and used to establish the identities (or the absence) of the metabolites. Studies with [18O]H2O demonstrate that the oxygens at positions 1 and 5 in the rearranged diol derive from molecular oxygen and water, respectively. Catalytic turnover of the enzyme is required for product formation from the olefin, but incubation of the epoxide metabolite with the enzyme, or with buffer alone, yields both the aldehyde and the rearranged diol products. The absence of trans-5-phenyl-2-penten-1-ol implies that the lifetime of the putative radical intermediate is so short that its existence as a discrete entity is questionable. A cationic intermediate is unlikely but cannot be excluded because the same metabolites are formed in a secondary reaction, even at pH 8.0, from the epoxide. The results provide no evidence for the involvement of radicals or cations in the epoxidation reaction, in agreement with results on the oxidation of olefins in organic solvents by metalloporphyrin catalysts.     

G2 effects of DNA-repair inhibitors on chromatid-type aberrations in root-tip cells treated with maleic hydrazide and mitomycin C

In recent years the existence of a DNA-repair process in G2 has been proposed to explain the potentiating effects of DNA-repair inhibitors given in G2 on chromatid aberrations (CA) induced by S-dependent as well as S-independent DNA-damaging agents. In the present report, root-tip cells of Allium cepa were exposed to maleic hydrazide (MH) or mitomycin C (MMC) and post-treated in G2 with caffeine (Caff) and various inhibitors of DNA synthesis. No enhancement of chromosome damage was observed when Caff was present in G2, but hydroxyurea (HU) or 5-fluorodeoxyuridine (FdUrd) potentiated the frequencies of CA. A slight additional increase of CA frequencies was observed following treatment with Ara C and excess thymidine in G2. When MH-damaged cells were pulse-treated with Caff earlier during recovery, the yield of CA was enhanced. The earlier Caff was present following MH treatment, the stronger was the potentiation.     

Embryos of different ages transferred to the rat oviduct enter the uterus at different times

Indirect evidence of embryo signalling to the oviduct was sought in rats by examining the transport of embryos of different ages. One-cell or four-cell embryos were transferred to the oviducts of recipient rats on Day 1 of pregnancy, and the number, condition, and location of native and transferred embryos was assessed on Day 4. To control for the effect of the presence of foreign embryos and excess number of eggs and the transfer procedure upon the fate of native embryos, other groups of rats were sham-operated or left undisturbed. Recipients had a mean number of ova significantly higher than controls. In controls and recipients of 1-cell embryos, the majority of eggs reached the morula stage and all of them were located in the oviducts. In those animals receiving 4-cell embryos, half of the eggs had reached the blastocyst stage and 28% were in the uteri (p less than 0.005). These results support the idea that advanced embryos can influence the timing of their entrance to the uterus in rats.     

Substrate oxidation by the heme edge of fungal peroxidases. Reaction of Coprinus macrorhizus peroxidase with hydrazines and sodium azide

The peroxidase from Coprinus macrorhizus is inactivated by phenylhydrazine or sodium azide in the presence of H2O2. Inactivation by phenylhydrazine results in formation of the delta-meso-phenyl and 8-hydroxymethyl derivatives of the prosthetic heme group and covalent binding of the phenyl moiety to the protein but not in the detectable formation of Fe-phenyl- or N-phenylheme adducts. Alkylhydrazines are catalytically oxidized but do not inactivate the enzyme. Catalytic oxidation of sodium azide produces the azidyl radical and results in its addition to the delta-meso position of the prosthetic heme group. Comparison of the heme adducts obtained with C. macrorhizus peroxidase with those generated by horseradish peroxidase shows that the regiochemistry of the addition reactions is the same in both cases. The results suggest that substrates interact primarily or exclusively with the heme edge rather than the ferryl oxygen of C. macrorhizus peroxidase and indicate that the interaction occurs with the same sector of the heme edge as in horseradish peroxidase. The active-site topologies of this pair of plant and fungal peroxidases thus appear to be similar, although the observation that alkylhydrazines add to the heme edge of horseradish but not C. macrorhizus peroxidase clearly shows that there are significant differences in the two active sites.     

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.     

Fertilized and unfertilized ova are transported at different rates by the hamster oviduct

To determine if the egg provides any clues for the regulation of ovum transport in the hamster, oocyte and embryo transport were compared. On the evening preceding ovulation, the animals were randomly assigned to one of five groups. They were caged overnight with a male of proven fertility (Group 1) or they were isolated (Group 2). Other females were artificially inseminated in both uterine horns at 2200 h either with fertile epididymal spermatozoa (Group 3), spermatozoa rendered infertile by freezing and thawing (Group 4), or with fertile spermatozoa in one uterine horn and infertile spermatozoa in the contralateral horn (Group 5). The number, condition, and distribution of ova in the genital tract were assessed at various intervals during the next 4 days. The rate of fertilization and normal development in females or sides inseminated with fertile or infertile spermatozoa was over 90% and 0% respectively. Embryos in Groups 1 and 3 reached the uterus 1 day earlier than unfertilized oocytes in Groups 2 and 4. In group 5, the transport of embryos resulting from insemination with fertile spermatozoa followed a pattern similar to those in Groups 1 and 3; the oocytes in the contralateral tract resembled those of Groups 2 and 4. The different transport rates of embryos and oocytes were not associated with the reproductive state of the female but with the condition of the ova. Moreover, the different transport rates were observed in animals transporting the two types of eggs simultaneously on different sides indicating that there is a local recognition of some unidentified factor unequally present in fertilized and unfertilized eggs.