Further Studies in Genetic Resistance of Fowl to RSV(RAV 0): Evidence for Interaction between Independently Segregating Tumour Virus b and Tumour Virus e Genes

The segregation of resistant and susceptible phenotypes in response to infection by RSV(RAV 2), RSV(RAV 50) and RSV(RAV 0), of avian RNA tumour virus subgroups B, D and E, respectively, was analysed in several test-crosses using chickens from the RPRL line 7-2, HPRS-synthetic line E and the Reaseheath line C. The results were fully consistent with out view reported previously that the genes at the tve and tvb loci segregate independently and recombine under the Mendelian second law of independent assortment. The dominant susceptibility es gene is expressed phenotypically when associated with the dominant susceptibility bs gene, but its expression is suppressed when associated with two doses of the recessive br gene. Genetic causes such as lack of penetration, recessive epistasis, and/or complementary intereaction between the tvb and tve genes have been discussed to account for the modified phenotypic expression of brbreses cells, i.e. resistance to subgroup E virus. Also, as reported previously, it was observed in this study that the tvb genes control the cellular response to subgroup D virus.