WHOLE GENOME SCAN FOR QUANTITATIVE TRAIT LOCI AFFECTING BODY-WEIGHT IN CHICKENS USING A 3 GENERATION DESIGN

An experimental population containing 10 full sib families of a cross between two broiler lines was created. In this population blood sample s from 20 full sib animals in generation 1 and 451 full sib animals in generation 2 were used for marker genotyping. Data on body weight at slaughter age (48 days) collected in a feed conversion experiment with 2049 individually housed grandoffspring was analysed. Large differenc es in mean and variance between male and female body weight were found . To account for these differences, a bivariate analysis treating body weight of males and females as separate traits was used to estimate ( co)variance components and breeding values. The model accounted for sy stematic environmental effects and maternal effects. The estimated her itability of body weight was 0.28 in the males and 0.33 in the females and the genetic correlation between male and female body weight did n ot significantly deviate from unity. Estimated breeding values, fixed and maternal genetic effects were used to calculate average adjusted p rogeny trait values for all generation 2 animals adjusted for fixed an d maternal genetic effects and for the additive genetic contribution o f the other parent. Male and female progeny trait values were combined in one trait value adjusting for sex differences by standardisation f or mean and variance. This average adjusted progeny trait value was us ed for QTL detection. To study presence of QTLs, an across family weig hted regression interval mapping approach was used both in half sib as well as a full sib QTL analysis. Genotypes from 368 markers mapped on 24 autosomal linkage groups were available. The most likely position for a QTL affecting body weight was found on chromosome 1 at 240 cM wi th a test statistic of 2.32. Significance levels were obtained using t he permutation test. The chromosomewise significance level of this QTL was 10%, whereas the genomewise significance level was 41%. New aspec ts of this study are: Genomewide QTL analysis in poultry, full sib ana lysis in an outbred population structure and correction for heterogene ous variances between sexes. (C) 1998 Elsevier Science B.V. All rights reserved.