Traits of economic importance are controlled by several genes and the environment. The detection of quantitative trait loci (QTL) and the genes underlying them are therefore important for the improvement of these traits. A study was conducted to locate putative candidate genes on GGAZ by orthologous comparison of QTL regions on GGAZ with the mouse and human genomes. Primer sequences from markers flanking QTL regions were blasted against the chicken genome using BLASTN (http://www.ensembl.org). Forty six chicken genes together with 91 mouse and 60 human genes were identified in this study. The annexin A1 gene, follistatin and neuronal acetylcholine receptor gene (nAChR) were some of the genes identified in this work. The nAChR gene is located at a QTL region for abdominal fat and could be used a therapeutic agent for feed intake and obesity. A second study was conducted to detect QTL regions for growth and skeletal traits in an F2 population selected for high and low growth. QTL for age-related body weight (BW), shank length (SL) and shank diameter (SD) were localized in 695 individuals. A pleitropic QTL on GGA4 explained 7-11% of the variance and affected BW at 5 to 9 weeks, and SL and SD at 9 weeks. A male -specific BW QTL was detected on GGA3 at 173 cM. The QTL on GGA4 had the strongest on SL and SD, and explained 18% and 21%, respectively of the variance. A third study located QTL for carcass composition and fat on GGA 2, 3, 4,5,10 and 26. Differentially expressed genes in the QTL regions included SOD and fat-1. The Spot 14 gene is associated with abdominal fat in chickens. The fourth study was conducted to characterize a major QTL region on GGA4 and to identify candidate genes in this region by CpG island detection and comparative mapping. One hundred and nine known genes and 179 CpG islands were located at this locus. Six putative novel genes were identified by blasting genes from 23 orthologous species against the chicken genome. A putative ortholog of the rhotekin gene was detected. Rhotekin is a housekeeping gene with acetylcholine activity.