Inheritance of fibrosarcomatous liver tumours in White Leghorn chicks inoculated vu the chorioallantoic membrane with subgroup A Rous sarcoma virus: A four‐allele genetic model

Abstract

An investigation was made using White Leghorn fowl to study the genetic control of subgroup A Rous sarcoma virus-induced fibrosarcomatous liver tumours (LT) in chicks inoculated via the chorioallantoic membrane (CAM). A total of 723 CAM-inoculated embryos were hatched in three experiments. In Expt 1, CAM-susceptibility and LT-mortality were examined on a within sire family basis to ascertain the inter-relationship between the two parameters. In Expt 2, sires that had records of high or low LT(+) deaths in the families were selected to produce progeny within high and low incidence lines in the next generation to ascertain the amenability of the trait (LT death) to selection pressure. Survivors of LT-assay (Expt 1) were mated inter se in Expt 3 to study the inheritance of the two traits according to known or proposed genetic models. It was shown that LT mortality is a genetic trait because of its amenability to selection, with a high realised heritability (h(2)(R)= 1.16). In the three experiments, most CAM-susceptibles (S) died of LT(+), and most CAM-resistants(R) survived, but there were some conversely associated phenotypes i.e. S(LT-) and R(LT+). The conventional 2-allele model of the tva (tumour virus a) locus with pleiotropic effect, or a 2-locus model with linkage, were considered inadequate to explain the occurrence of conversely associated phenotypes on a within family basis. However, a 4-allele model of the tva locus showed a good fit to the results of this study.