Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: June 13, 1996
Publication Date: N/A
Technical Abstract: Selection projects that originate with a composite population provide a powerful resource for mapping quantitative trait loci (QTL) if the favorable allele at a QTL originates from only one of the breeds used to make the composite and marker allele frequencies differ among breeds. Marker allele frequencies in selected animals that differ from values expected by chance indicate that the marker is near a QTL. To test the efficiency of this approach, 1000 replications of a selection project originating from a 3-breed composite were simulated. To form the composite, breed S was mated to H and the S x H F1 subsequently mated to breed C. The favorable QTL allele was simulated to originate from S. Markers were simulated every 10 cM across 29 chromosomes. Each chromosome was 100 cM in length. The number of reproducing females in inventory was 180. Randomly chosen females reproduced first at 1 year of age and were culled subsequently based on age to minimize average age and hold numbers of breeding females at 180. Males didn't reproduce until 2 years of age to permit recording of phenotypes. The top 14 males were selected for breeding and genotyped. The allele substitution effect for the QTL was 1 SD. Selection was carried out for 7 years. The marker with the highest log-likelihood statistic correctly identified the chromosome containing the QTL in 95% of the replications. This same success rate could be achieved for a QTL with an effect of .5 SD if selection was carried out for 15 years instead of 7. Clearly, successful mapping using this approach depends on accumulated genetic change rather than the effect of the QTL.