Genetic evaluation and selection in multibreed populations
Lo, Ling-Ling
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Permalink
https://hdl.handle.net/2142/22306
Description
Title
Genetic evaluation and selection in multibreed populations
Author(s)
Lo, Ling-Ling
Issue Date
1994
Doctoral Committee Chair(s)
Fernando, Rohan L.
Department of Study
Animal Sciences
Discipline
Animal Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Genetics
Language
eng
Abstract
Crossbreeding is used widely in animal production, thus theory and methods for genetic evaluation and selection are required for multibreed populations. This study developed theory for modelling genotypic means and covariances which are required to obtain genetic evaluation by best linear unbiased prediction (BLUP) for multibreed populations. Theory and methods for genetic evaluation and selection by BLUP using the multibreed covariance theory were presented, and the effects of using this covariance theory for genetic evaluation and selection were studied. With additive inheritance, the covariance between crossbred relatives can be computed using the formula for a purebred population, provided that the variance of crossbred individuals are computed correctly. The additive variance for a crossbred individual is a function of additive variances for the pure breeds, the covariance between parents, and segregation variances. The segregation variance is the genetic variance derived from the differences in allelic frequencies between pure breeds. An efficient algorithm to compute the inverse of the additive covariance matrix was also given. With dominance inheritance, the covariance between relatives in a multibreed population is a linear function of identity coefficients, coefficients of breed origin, and 25 dispersion parameters. A recursive procedure was given to compute the necessary identity coefficients. Genetic evaluations were obtained by BLUP via Henderson's mixed model equations. Constructing these equations requires the inverse of the multibreed covariance matrix. However, an efficient method to invert this covariance matrix has not yet been developed. Thus, alternative mixed model equations were presented for obtaining genetic evaluations efficiently in two-breed and three-breed terminal crossbreeding systems. Numerical examples were used to illustrate the multibreed evaluation procedures. Multibreed covariance theory under dominance inheritance was validated by comparing a covariance matrix estimated from simulated data with the theoretical covariance matrix. Selection index theory and computer simulation were used to study the advantage of using multibreed covariance theory for genetic evaluation and selection. A significant advantage was observed when differences in allelic frequencies between the pure breeds were large and the degree of dominance was greater than or equal to one. Results from this study suggested that use of multibreed covariance theory for genetic evaluation and selection may be most useful for low heritability traits such as fertility traits.
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