Review of QTL mapping results in chickens

A review of QTL for production, behaviour and disease resistance traits published to the end of 2004 is presented. QTL were located randomly over the genome and there was little commonality between different studies for similar traits. However, there were several reports of QTL from different experiments in similar regions of chromosomes I (at 250 and 450 cM), 4 and 8 and for disease resistance on chromosome 5. Generally there were 6 to 8 QTL affecting the major production traits in experimental breed crosses and collectively they accounted for a substantial proportion of the line difference where this information was provided. The size of typical genome-wide significant effects for production traits was 0.3 to 1.0 phenotypic standard deviations. Genetic effects for growth traits were generally additive whereas about one-third of QTL for other production traits showed significant dominance effects. Variable reporting standards were noted and proposals for minimum published information are presented. Currently there are scientific opportunities for meta-analyses of results from experiments on body weight gain and considerable potential for combining data and results from different studies for other traits in the future.