CFTR and cystic fibrosis: In this work the CftrTgH(neoim)Hgu insertional mutation was backcrossed from CF/3-CftrTgH(neoim)Hgu onto the inbred backgrounds C57BL/6J and DBA/2J generating congenic animals in order to clarify the differential impact of the Cftr mutation and the genetic background on the disease phenotype of the cystic fibrosis mutant mice.