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Genetic Evaluation Under an Animal Model When Identical Genotypes Are Represented in the Population¹

University of Guelph², Guelph, Ontario, Canada N1G 2W1

Abstract

Use of split embryos and other forms of cloning as well as the natural occurrence of monozygotic twins results in animals in the population that are genetically identical. This can complicate genetic evaluation under an animal model because the matrix of additive genetic relationships among animals, A, is singular and A^–1 does not exist. Solution of mixed model equations with singular A is computationally difficult and is feasible only for small populations. It is shown algebraically and illustrated through a numerical example that defining A as the matrix of additive genetic relationships among genotypes, rather than animals, and treating records on clones as repeated records on the same genotype allows use of the usual mixed model procedures for nonsingular A and is computationally simpler and feasible for large populations. Results are shown to be identical to those obtained through use of the more difficult procedures for singular A.

¹ Financial support was provided by the Canadian Assoc. of Anim. Breeders, the Nat. Sci. and Eng. Res. Council of Canada and the Ontario ministry of Agric. and Food.

² Centre for Genet. Improv. of Livest.