8.11.1: Effect of additional information on the accuracy
The more information is available related to the genetics of an animal, the more accurate the EBV. Information on offspring is highly valuable because they share the true half of the genes with their parent. But for young animals that is no realistic source of information yet. In the absence of information of full or half sibs, their parents are the only source of information. They share the true half of their genes with their offspring, and thus should be highly valuable as information source. However, there is a complicating factor with information of parents, because due to Mendelian sampling you do not know WHICH half if the genes are passed on. This is different from (multiple) offspring as information source, because there you do know that half of the genes are passed on. Under the assumption of an average other parent of the offspring the genetic potential (TBV) of the animal can be estimated quite accurately. The fact that each offspring receives one half of the genetics of the animal, but each may receive a slightly different half, makes it possible to quantify the Mendelian sampling component and get an accurate estimate of the EBV. Still the accuracy will depend on the number of offspring and the heritability.
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Thus: information on offspring is more valuable than that of sibs because the offspring receives half of the genes from the animal. If sufficient number of offspring are available then the Mendelian sampling effect can be quantified and the EBV of the animal can be estimated very accurately.