فهرست نشریات علمی دسترسی آزاد ایران

So far, the parent-of-origin genetic effects have not been accounted for analyzing the sexual size dimorphism (SSD) in sheep. Therefore, genetic analysis of sexual size dimorphism in Baluchi sheep was performed with models incorporating the parent-of-origin genetic effects. Body weights at birth (BW), weaning (WW), 6 (W6), 9 (W9) and 12 (W12) months of age were analyzed with twelve bivariate animal models including the male and female body weight records as different traits. Male lambs were 0.26, 1.92, 3.049, 3.228, 4.695 kg heavier than females at birth, weaning, and 6, 9 and 12 months of age, respectively. The SSD level (expressed as male/female ratio) was 1.062, 1.085, 1.11, 1.11 and 1.13 for BW, WW, W6, W9 and W12, respectively. For all traits studied, a model that contained the maternal imprinting effects was selected as the most appropriate one. For BW and WW, maternal imprinting heritability ( ) was higher in males (0.25 and 0.12) compared to females (0.21 and 0.11), but for W6, W9 and W12, females recorded higher   (0.24, 0.34, 0.27 vs. 0.12, 0.22, 0.17). The estimates of direct heritability ( ) were almost equal in both sexes ranging from 0.02 (W6) to 0.15 (W12) in males and 0.03 (W6) to 0.16 (W12) in females. For all traits studied, maternal permanent environmental and residual variances were greater in males than females, indicating greater environmental sensitivity of male lambs. Cross-sex additive genetic correlation, maternal imprinting correlation, and maternal permanent environmental correlations were close to unity indicating absence of sexual dimorphism for direct additive, maternal imprinting, and maternal permanent environmental effects on the traits studied. Therefore, divergent selection could not be recommended because selection for either male or female weights would result in a strongly correlated response in the other sex.