REVEALING GENE-ACTION FOR PRODUCTION CHARACTERISTICS BY INBREEDING, BASED ON A LONG-TERM SELECTION EXPERIMENT

The gene action involved in the expression of production characters wa s investigated, using the effect of the theoretical inbreeding coeffic ient on the mean of the characters in a two-way selection experiment f or the slope (b) and intercept (ln (a)) of the allometric function: w = ln (a) + bv [where w = ln (body mass) and v = ln (cumulative feed in take)]. From Crow & Kimura's (1970) finding that three possibilities e xist when the change in the mean of a character is plotted against the inbreeding coefficient (F), it was decided to plot the means of the c haracters under investigation against F, and to fit regressions to det ermine whether no dominance, dominance without epistasis, or dominance with epistasis were involved in the expression of these characters. I t was found that dominance may be involved in all the examined charact eristics except the intercept (Phase 2) and slope (Phase 2) of the all ometric model and average daily feed intake (Phase 1) of the ln (a) se lection group, as well as average daily feed intake (Phase 1 and 2) of the b selection group.