Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/1997
Publication Date: N/A
Interpretive Summary: Marek's disease (MD) is an economically-important disease of chickens. Currently, vaccines have controlled the problem but new emerging strains of the disease-causing virus which vaccines cannot control are being encountered more frequently. To help combat MD, chickens are being selected for genetic resistance. Biotechnology may greatly enhance the rate of poultry breeding improvement by identifying the genes responsible for conferring resistance. In this study, eight regions in the chicken genome were identified that contain MD-resistance genes. The genes in these regions could account for up to 66% of the genetic resistance. The results will eventually lead to cloning of the responsible genes. Ultimately, the poultry industry will benefit by using DNA markers that can indicate which animals are genetically resistant.
Technical Abstract: Marek's disease (MD) is a lymphoproliferative disease caused by a member of the herpesvirus family. Diseased chickens infected by the MD virus (MDV) commonly exhibit paralysis, blindness, and lymphoid tumors. The development of a genetic map of the chicken enabled us to identify quantitative trait loci (QTL) affecting susceptibility to MD. The inbred lines 63 (MD resistant) and 72 (MD susceptible) were mated to create 300+ F2 chickens. The F2 chickens were challenged with JM strain MDV at 1 week of age and monitored for symptoms of MD up to 10 weeks of age. A multistage approach was used for QTL mapping. In stage 1, 65 DNA markers from the East Lansing genetic map were typed on 40 of the most MD susceptible and MD resistant F2 chickens, and 21 markers (P less than or equal to 0.20) residing near suggestive QTL affecting MD susceptibility were revealed by ANOVA. In stage 2, the suggestive markers plus flanking markers were typed on 272 F2 chickens, and four suggestive QTL (P less tha or equal to 0.0016) were identified by ANOVA. In stage 3, using a suite of interval mapping programs, eight genomic regions with closely linked QTL affecting several components of MD susceptibility were identified. In stage 4, using multivariate approaches of QTL analysis, three to six loci collectively explained between 12 and 23% of the total phenotypic MD variation, or 34 to 66% of the genetic variance. The majority of the QTL were recessive with respect to the Line 72 allele. It appears that interaction between loci are significant in the expression of MD susceptibility. This study sheds light on the multigenic basis of MD susceptibility in the chicken, and provides a model for elucidating viral disease susceptibility genes in other vertebrates, including humans.