Mutations in the CI gene of lambda bacteriophage which retain immunity and confer a rex phenotype.
D002874:Chromosome Mapping; D003090:Coliphages / Q000276:immunology*; D005827:Genetics, Microbial; D007109:Immunity; D008242:Lysogeny; D009154:Mutation; D010641:Phenotype; D013045:Species Specificity