Records on growth and reproductive characteristics collected from 1993 to 2013 at the Breeding Station of Kermani sheep, south-east of Iran, were used for estimating genetic parameters related to parent-of-origin effects. The studied growth traits were birth weight (BWT), weaning weight (WWT), six-month weight (6MW), average daily gain from birth to weaning (ADG1), and average daily gain from weaning to six months of age (ADG2). The reproductive traits were litter size at birth per ewe lambing (LSB), litter size at weaning per ewe lambing (LSW), the sum of litter weight at birth per ewe lambing (LWB), and the sum of litter weight at weaning per ewe lambing (LWW). Models with and without imprinting (maternal and paternal) effects were compared by applying Akaike's information criterion (AIC). Maternal imprinting effects explained 14, 7, 24 and 5% of the phenotypic variances for BWT, WWT, 6MW and ADG1, respectively and their inclusion in the model decreased direct heritability estimates for BWT (from 0.07 to 0.05), WWT (from 0.29 to 0.23), 6MW (from 0.26 to 0.12) and ADG1 (from 0.20 to 0.17). Imprinting effects did not affect ADG2 and studied reproductive traits. The results indicated that a considerable proportion of the maternal imprinting effects overlap with direct additive genetic and maternal effects. Therefore, imprinting effects may be crucial for the genetic assessment of BWT, WWT, 6MW and ADG1 in Kermani sheep.

The X chromosome is known to play an important role in many sex-specific diseases. However, only a few single-nucleotide polymorphisms on the X chromosome have been found to be associated with diseases. Compared to the autosomes, conducting association tests on the X chromosome is more intractable due to the difference in the number of X chromosomes between females and males. On the other hand, X-chromosome inactivation takes place in female mammals, which is a phenomenon in which the expression of one copy of two X chromosomes in females is silenced in order to achieve the same gene expression level as that in males. In addition, imprinting effects may be related to certain diseases. Currently, there are some existing approaches taking X-chromosome inactivation into account when testing for associations on the X chromosome. However, none of them allows for imprinting effects. Therefore, in this paper, we propose a robust test, ZXCII, which accounts for both X-chromosome inactivation and imprinting effects without requiring specifying the genetic models in advance. Simulation studies are conducted in order to investigate the validity and performance of ZXCII under various scenarios of different parameter values. The simulation results show that ZXCII controls the type I error rate well when there is no association. Furthermore, with regards to power, ZXCII is robust in all of the situations considered and generally outperforms most of the existing methods in the presence of imprinting effects, especially under complete imprinting effects.