Intercrosses in Chickens. Doctor’s dissertation.

Most phenotypes in human and animals have a multifactorial background, e.g. they depend on many different genes and environmental factors may play a prominent role. Geneticists have long been concerned with identifying key genes responsible for variation in multifactorial traits, such as obesity and diabetes in humans and production traits in animals. In this thesis I have used two different intercrosses to map Quantitative Trait Loci (QTL) for growth and production traits in chicken. The first part of the thesis is based on an intercross between White Leghorn and the ancestor of the modern domesticated chicken, the red junglefowl. A total of 13 QTLs reached genome-wide significance and the four major QTLs explain around 80 % of the phenotypic variance between the parental populations in males, indicating that a few QTLs have had a large influence on the enhanced growth rates in domesticated chickens. The second intercross is between two chicken lines divergently selected for body weight at 56 days of age. The selection response has been remarkable and after 42 generations of selection the lines differ almost nine-fold in weight. QTL studie