Several genetic engineering approaches can and will be used to control viral diseases in chickens. One approach is to insert genes for resistance in the germ line of the chicken. The endogenous avian leukosis virus (ALV) genes that segregate in the chicken serve as a natural model for germ line insertion and expression. One gene controls the expression of endogenous ALV envelope antigen. Chickens carrying that gene are resistant to infection with endogenous ALV. We propose, as a model, to insert the envelope gene of exogenous ALV, thus inserting a dominant gene for resistance to exogenous ALV. Our approach to germ line insertion in the chicken, including insertion methods, vectors and testing, is discussed. Genetic engineering approaches to animal breeding will only be useful as methods to enhance the efficacy of present breeding methods. Gene insertion can add new genetic variation by crossing the species barrier, and by introducing genes into highly productive lines one at a time. Molecular methods may also be useful for the introduction of chromosomal markers and to help identify major genes influencing phenotypes controlling productive efficiency. Key words: Germ line, vectors, retrovirus, chicken, endogenous virus, lymphoid leukosis
Domestic chickens activate a piRNA defense against avian leukosis virus