Quantitative trait loci (QTL) for growth and egg traits were identified in chickens. After parentage checking,
data of F2 chicks must be genotyped using genetic markers in the autosomal linkage groups and Z chromosome
and the genotypes were used for QTL analysis. A mixed model included the fixed effects along with the additive
and dominance effects of QTL as random effects were used for QTL analysis. In an Egyptian recent study, the
total map length was 1901 cM for growth traits and 1949 cM for egg traits. A total of 34 QTL were detected for
body weight traits (BW) where these QTL were distributed over five distinct regions on 10 chromosomes, and
their effects ranged from 1.2 to 13.8% of the phenotypic variation. In this study, a total of 19 significant genome
QTL that affected body weights were located on seven macro-chromosomes (1, 2, 3, 4, 6, 8 and Z) and one microchromosome
(11). The proportions of phenotypic variation explained by significant and suggestive QTL for body
weight traits at 4, 8, 12 and 16 weeks were 21.1, 30.8, 29.3 and 25.4%, respectively. The additive effects of QTL
on growth traits were positive, while the dominance effects were generally negative or not significant. A QTL for
body weight at 12 weeks of age segregating on chromosome 4 had the largest additive effect and explained 13.8%
of the phenotypic variation, while the largest dominance effect for QTL on chromosome 4 and accounted for 6.5%
of the phenotypic variation. The QTL effects were found on chromosomes 2, 4, 8 and Z for weight at first egg
(WFE), on chromosomes 3 and Z for age at first egg (AFE), on the chromosomes 4 and Z for egg weight, on the
chromosomes 4 and Z for egg number (EN). The QTL effects expressed as the percentage of the phenotypic
variance explained by each QTL were mostly of considerable importance ranging from 1 to 6.9 % of the
phenotypic variation for WFE, 5 to 7.2 % for AFE, 5.6 to 13 % for EW and 3.6 to 5 % for EN. The whole genome
scan for detection and localization of QTL affecting egg quality traits were described. |
