Directionality and nonreciprocality of Chi-stimulated recombination in phage lambda

Chi's are genetic elements that stimulate generalized recombination in their locale in phage lambda. All Chi's wherever located on lambda's chromosome, act asymmetrically in crosses blocked in DNA replication: (1) They stimulate exchange primarily to their left on the conventional lambda map, and (2) the stimulated exchange is frequently nonreciprocal, the recombinant carrying the Chi element being produced less often than the complementary product.