Genetical Research

Many QTLs with minor additive effects are associated with a large difference in growth between two selection lines in chickens

a1 Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, BMC, SE-75124 Uppsala, Sweden
a2 Department of Medical Biochemistry and Microbiology, Uppsala University, BMC, SE-75124 Uppsala, Sweden
a3 Department of Neuroscience, Uppsala University, BMC, SE-75124 Uppsala, Sweden
a4 Institut Català de Recerca i Estudis Avançats, 08010 Barcelona, Spain
a5 Department de Ciència Animal i del Aliments, Facultat de Veterinária, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
a6 Virginia Polytechnic Institute and State University, Department of Animal and Poultry Sciences, Blacksburg, VA 2406-0300, USA

Article author query
jacobsson l   [PubMed][Google Scholar] 
park hb   [PubMed][Google Scholar] 
wahlberg p   [PubMed][Google Scholar] 
fredriksson r   [PubMed][Google Scholar] 
perez-enciso m   [PubMed][Google Scholar] 
siegel pb   [PubMed][Google Scholar] 
andersson l   [PubMed][Google Scholar] 


Two growth-selected lines in chickens have been developed from a single founder population by divergent selection for body weight at 56 days of age. After more than 40 generations of selection they show a nine-fold difference in body weight at selection age and large differences in growth rate, appetite, fat deposition and metabolic characteristics. We have generated a large intercross between these lines comprising more than 800 F2 birds. QTL mapping revealed 13 loci affecting growth. The most striking observation was that the allele in the high weight line in all cases was associated with enhanced growth, but each locus explained only a small proportion of the phenotypic variance using a standard QTL model (1·3–3·1%). This result is in sharp contrast to our previous study where we reported that the two-fold difference in adult body size between the red junglefowl and White Leghorn domestic chickens is explained by a small number of QTLs with large additive effects. Furthermore, no QTLs for anorexia or antibody response were detected despite large differences for these traits between the founder lines. The result is an excellent example where a large phenotypic difference between populations occurs in the apparent absence of any single locus with large phenotypic effects. The study underscores the need for powerful experimental designs in genetic studies of multifactorial traits. No QTL at all would have reached genome-wide significance using a less powerful design (e.g. approx. 200 F2 individuals) regardless of the nine-fold phenotypic difference between the founder lines for the selected trait.

(Received May 16 2005)
(Revised August 22 2005)

c1 Department of Medical Biochemistry and Microbiology, Uppsala University, BMC, Box 597, SE-75124 Uppsala, Sweden. Tel: +46 18 4714904. Fax: +46 18 4714833. e-mail: