Weight gain and heterosis at different stages of development of the rat.

Diallel crosses among four highly inbred lines of rats were made in order to evaluate their combining ability at 10 day intervals during postnatal growth. Analyses were undertaken to consider the relative magnitudes of different components of variation, including a heterotic effect, over a long developmental period. A general analysis of variance for least square means of body weights indicated that postnatal growth was influenced greatly by the maternal lines and to a lesser extent by the paternal line. Heterosis was measured as a statistically significant difference in body weight gain at 10 day intervals between the hybrid and either the averaged mean of the parent lines or the mean of the largest parent line. Of the effects analyzed, heterosis accounted for a major part of body weight variability in both sexes between 30 and 100 days of age but reached much higher levels in male than in female progeny. The heterotic response was most pronounced during the rapid growth phase; that is, between the ages of 20 to 50 days. Although interesting specific exceptions were observed, heterotic responses generally became more pronounced with increasing age through 100 days. Evidence for differential heterosis associated with particular lines was present in male progeny at growth stages immediately preceding and following the phase of most rapid growth. Specific combining ability, however, was generally lacking. Analyses of specific matings indicated that heterosis, in the lines tested, is a variable phenomenon which may be dependent upon the degree of genetic divergence between inbred parent lines and the combining ability of the genotype involved.

Measurement of the generalized polarizabilities of the proton in virtual Compton scattering at Q2=0.92 and 1.76 GeV2.

We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions P(LL)-P(TT)/epsilon and P(LT), and the electric and magnetic generalized polarizabilities (GPs) alpha(E)(Q2) and beta(M)(Q2) at momentum transfer Q(2)=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q2, compensated at higher Q2 by a paramagnetic contribution from piN intermediate states.

Dynamics of the 16O(e, e'p) reaction at high missing energies.

We measured the cross section and response functions for the quasielastic 16O(e,e'p) reaction for missing energies 25< or =E(m)< or =120 MeV at missing momenta P(m)< or =340 MeV/c. For 25