The effect of pedigree structure on estimation of variance components and genetic parameters of a quantitative trait in sheep

In the present study، the effect of incomplete sire’s pedigree on variance component، genetic parameters and accuracy of selection for a quantitative trait in sheep were studied using computer simulation. Two populations with heritability’s of 0. 15 and 0. 30 for a hypothetic quantitative trait were simulated. Data including animal ID، Sire ID، Dam ID، phenotypic values، additive genetic values and environmental values were saved for two populations. Sire numbers were deleted with proportions of 0، 10، 20، ….. ، 100 percentage of total pedigree. Deletion of sire numbers were done randomly and sequentially and the resulted files in each case were saved. In order to estimation of variance components and genetic parameters and prediction of breeding values، data were analyzed with simple animal model using DFREML package. In population 1 (h2=0. 15) and the case of random deletion، phenotypic variance was approximately constant as the deletion percentage of sires increased. Additive genetic variance decreased and error variance increased partially. Consequently، h2 reduced، but the changes were not significant (P>0. 05). The accuracy of selection () were significantly reduced from 0. 666 (complete pedigree) to 0. 483 (without sires pedigree). The trend of variance components and heritability’s in population 2 (h2=0. 30) were the same as population 1، but the changes of heritability’s were significant. The accuracy of selection () were significantly reduced from 0. 850 (complete pedigree) to 0. 685 (without sires pedigree) in population 2. In case of sequential deletion of sire’s pedigree، the trend of variance components and heritability was approximately constant in population 1. The estimates of heritability were non significantly reduced based on increasing of deletion percentages of sire’s pedigree. Generally، the results of this study showed that the amount of sire’s pedigree deletion affected variance components، heritability and the accuracy of selection.