CROSSBREEDING EFFECT ON SEXUAL DIMORPHISM OF BODY-WEIGHT IN INTERGENERIC HYBRIDS OBTAINED BETWEEN MUSCOVY AND PEKIN DUCK

From a factorial crossbreeding experiment between two Muscovy and Peki n duck strains it appears that the increased body weight sexual dimorp hism in favour of males in the Muscovy growing duck depends on this Mu scovy mother in pure breds and in the reciprocal cross. The ratio of m ale to female body weight averages took the values of 1.19, 1.47, 1.75 , 1.77, 1.84 and 1.64, respectively, at 4, 10, 16, 20, 30 and 40 weeks of age in the Muscovy progeny. This tendency was similar in the Pekin x Muscovy progeny. On the contrary this ratio took the values of 1.07 and 1.11 at 10 and 16 weeks of age in the Pekin progeny, being simila r in the Muscovy x Pekin progeny (1.06 1.07 and 1.08, respectively, at 16, 20 and 30 weeks of age). These results are evidence of a contribu tion of the Muscovy female duck to increase the body weight sexual dim orphism in duck by depressing the body weight growth in female progeny and not in the male progeny either in pure or crossbreeding. If the m aternal effects are assumed to tie similar in male and female progeny, the ranking of the four genotypes in the female progeny could be expl ained by adding to the effect of sex-linked genes (Z chromosome) the e ffect of genes on the W chromosome. Within a Mendelian inheritance pat tern it may be suggested that, besides the usual sex-linked gene effec ts, coding genes of the non-pseudo-autosomal region (NPAR) of the Musc ovy W chromosome depress growth when compared to the Pekin W chromosom e. (C) Inra/Elsevier, Paris.