LX4 is one the most important genotypes of infectious bronchitis coronavirus worldwide. Two LX4 genotype viruses have novel genomic organizations which lacked 3a and 5b gene, respectively. Recombination events may be responsible for the emergence of the LX4 genotype. Most of these viruses disappeared likely because they were not “fit” to adaptation in chickens. The “fit” viruses continued to evolve and have become widespread and predominant in commercial poultry.