2010-Casellas_et_al - Accounting for additive genetic...

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J. Casellas, G. Caja and J. Piedrafita Accounting for additive genetic mutations on litter size in Ripollesa sheep 2009-12-18T10:46:06-08:00; 2010, 88:1248-1255.doi: 10.2527/jas.2009-2117 originally published online J ANIM SCI http://jas.fass.org/content/88/4/1248 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 May 22, 2011 jas.fass.org Downloaded from
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ABSTRACT: Little is known about mutational vari- ability in livestock, among which only a few mutations with relatively large effects have been reported. In this manuscript, mutational variability was analyzed in 1,765 litter size records from 404 Ripollesa ewes to character- ize the magnitude of this genetic source of variation and check the suitability of including mutational effects in genetic evaluations of this breed. Threshold animal models accounting for additive genetic mutations were preferred to models without mutational contributions, with an average difference in the deviance information criterion of more than 5 units. Moreover, the statis- tical relevance of the additive genetic mutation term was checked through a Bayes factor approach, which showed that the models with mutational variability were 8.5 to 22.7 times more probable than the others. The mutational heritability (percentage of the pheno- typic variance accounted for by mutational variance) was 0.6 or 0.9%, depending on whether genetic domi- nance effects were accounted for by the analytical mod- el. The inclusion of mutational effects in the genetic model for evaluating litter size in Ripollesa ewes called for some minor modifications in the genetic merit order of the individuals evaluated, which suggested that the continuous uploading of new additive mutations could be taken into account to optimize the selection scheme. This study is the first attempt to estimate mutational variances in a livestock species and thereby contribute to better characterization of the genetic background of productive traits of interest. Key words: animal breeding, genetic variability, litter size, mutation, Ripollesa breed ©2010 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2010. 88:1248–1255 doi:10.2527/jas.2009-2117 INTRODUCTION As discussed by Goddard (2001), the standard infini- tesimal model used for genetic evaluations of a given phenotypic trait of interest simplifies its genetic back- ground to a large number of genes with small and ad- ditive effects. These additive effects are also related to the genetic variability present in the founder popula- tion (Henderson, 1973), in which mutations that arise in further generations are assumed not to exist. Sources of variation such as nonadditive effects or mutation are commonly omitted, although multiple analytical ap- proaches accounting for these biological phenomena have been developed in recent decades (Wray, 1990; Varona and Misztal, 1999).
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2010-Casellas_et_al - Accounting for additive genetic...

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