The effect of linkage on the additive by additive covariance between relatives

The additive x additive relationship coefficient needs to be calculated in order to compute genetic covariance between relatives. For linked loci, the computation of this coefficient is not as simple as for unlinked loci. Rec ursive formulae are given to compute the additive x additive relationship c oefficient for an arbitrary pedigree. Based on the recursive formulae, nume rical values of the desired coefficient for selfed or outbred individuals a re examined. The method presented provides the means to compute the additiv e x additive relationship coefficient for any situation assuming linkage. T he effect of linkage on the covariance was examined for several pairs of re latives. In the absence of inbreeding, linkage has no effect on the parent- offspring covariance. All of the other relationships examined were affected by linkage. As recombination rate increased from 0.1 to 0.5, in descending order of percentage change in the covariance, the relationships ranked as follows: first cousins, double first cousins, grandparent-grandoffspring, h alf sibs, aunt-nephew, full sibs, parent-offspring. With inbreeding, the pa rent-offspring covariance is also affected by linkage. (C) Inra/Elsevier, P aris.