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2009-Kearney_et_al - Consequences of selection for...

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J. F. Kearney, P. Navarro, C. S. Haley and B. Villanueva deleterious alleles for fitness Consequences of selection for improving production traits on the frequency of doi: 10.2527/jas.2008-1099 originally published online November 7, 2008 2009, 87:850-859. J ANIM SCI http://jas.fass.org/content/87/3/850 the World Wide Web at: The online version of this article, along with updated information and services, is located on www.asas.org by guest on October 11, 2011 jas.fass.org Downloaded from
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ABSTRACT: In this study the effect of artificial selection on BLUP EBV for production traits on the allele frequencies of a pleiotropic QTL affecting both production and disease susceptibility was investigated. Stochastic simulations were used to model artificial se- lection on a production trait that is controlled, in part, by a biallelic QTL that also controls susceptibility to disease. The QTL allele increasing production also in- creased susceptibility to disease. Different modes of ac- tion and proportions of variation accounted for by the QTL were assessed for the production trait. The main results indicated that alleles that confer susceptibility to the disease could be maintained in the population over a long period, depending on the mode of action of the QTL. In addition, the results of the study indicate that, under various conditions, it is possible to find pleiotropic QTL that control 2 traits despite these traits appearing to be uncorrelated. Therefore, in practice, an estimate of the genetic correlation between 2 traits may be misleading when the presence of such a QTL exists. The results of this study have implications for breeding programs. For example, if a pleiotropic QTL exists that favors heterozygotes for a production trait, it would be very difficult to remove disease susceptibility alleles via traditional selection methods. Key words: fitness, health-related trait, pleiotropy, quantitative trait locus, selection ©2009 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2009. 87:850–859 doi:10.2527/jas.2008-1099 INTRODUCTION In domestic livestock species, improving health-relat- ed traits has become increasingly important (Bishop et al., 2002). To evaluate the benefits of including health- related traits in the breeding objective, it is necessary to know their genetic relationships with other traits of importance such as production traits. It is generally ac- cepted that if the estimated additive genetic correlation between production and disease susceptibility is zero, improvement in production traits can be accomplished without adversely affecting the disease trait (Falconer and Mackay, 1996). Most QTL mapping experiments have focused on pro- duction traits, although QTL for health-related traits may offer more benefits (e.g., Dekkers, 2004). Mapping studies aimed at finding QTL for these low heritabil- ity traits could easily have production data available, allowing the search for pleiotropic QTL to be used in marker-assisted selection programs.
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