Genetic differences among chicken embryos in response to inoculation with an isolate of infectious bronchitis virus.

Fowls differ genetically in their ability to resist invasion by many parasites including viruses, bacteria, fungi, protozoa, and helminths. Genetic differences have been demonstrated among breeds, among strains of the same breed, and even among families (11,20). By studying the reciprocal crosses of the resistant and susceptible lines, genetic resistance has been demonstrated to coccidiosis (18), pullorum disease (17), and Newcastle disease (16). The effect of the sire was greater than that of the dam, suggesting possible sex linkage, but the differences were not statistically significant. The decrease in the weight of the body and the visceral organs due to vaccination with Newcastle disease (ND) virus is different for different strains of birds (7). In very few instances has the actual mode of inheritance to disease been demonstrated. In mice the gene for resistance to some Arboviruses is dominant and autosomal, whereas in mouse hepatitis the gene for susceptibility seems to be dominant. The susceptibility to hepatitis and Arboviruses (Group B) is of a cellular nature, since results similar to the above were obtained in cell culture (8,12). In fowls the mode of inheritance has been established for resistance to Rous sarcoma virus (RSV) (2,3,19) and erythroblastosis virus (20). In both instances, inheritance is by a single auto-