REPRODUCTIVE-PERFORMANCE IN A COMPLETE DIALLEL CROSS AMONG LONG-TERM SELECTED MOUSE LINES

Aim of the present study was to investigate the influence of long-term pure-bred selection with respect to combining ability of several line s of mice. Four lines were formed from Fzt:DU-outbred-strain Selection criteria of three lines were litter size and litter weight at birth ( line F:73 generations), body weight at 6 weeks (line G:52 generations) , treadmill performance (E:28 generations); the fourth line was a cont rol line C. Complete diallel crosses of these lines were set up in two environments (keeping conditions). Data of single crosses were analys ed by GLS. For estimation of crossbreeding effeects different fixed ef fects models are used. Litter size and litter weight at birth were ana lysed. - Means The largest positive line effects are found for litter size and litter weight in all crossbreds with line F, especially if F is the dam line. For crosses with F in both traits and environments he terosis effects are frequent. Best combinations are G x F (male, femal e) and F x G. Good results are also observed if line G is used as pare ntal line. The lines E and C have a worse effect on the performance of their F-1 crosses. The worst combination of the diallel is C x E. - F ixed effects of diallel model given by GRIFFING and by EBERHART/GARDNE R As expected as a consequence of the selection for litter size and li tter weight at birth line F had the highest general combining ability g(i) (including average direct genetic and line heterotic effects) for litter size in both environments. Ranking of the lines for g(i) line G took the second place because of the positive correlated response ex hibited in litter size due to growth selection. Negative g(i) were obs erved in the control and in line E. In specific combining ability (s(i j)) there are similarities between the models in tendency, but differe nces are between the environments. In both models crosses between F an d G have the highest s(ij) in environment 1; in environment 2 the cros ses F x E and E x F are the bests. - Fixed effexts of the diallel mode l given by EISEN et al. As expected in both environments line F had th e highest positive response in average direct genetic effect (ii) in l itter size followed by line G. Negative effects were noticed for line E and C. The average maternal genetic effects (m(i)) of the lines were different between the environments and mostly lower than for direct e ffects. Litter size had different ranking of lines in the two environm ents: F>C>E>G (environment 1); E>G>F>C(environment 2). Overall direct heterosis (($) over bar h) estimates for litter size were equal in bot h environments. All populations showed some degree of line heterosis ( h(i)) only in lines F and G positive effects were given in both enviro nments. Specific direct heterosis (S-ij) varied among crosses and envi ronments. Positive values in both environments were shown only by G x E ind F x C and their reciprocals. Specific reciprocal effects (r(ij)) differed between crosses and environments. For litter size they did n ot show biological relevance.