Describe the difference between a Hfr cell and a F+ cell. If an environmental change leads to the repression on N in the Lambda phage, describe the mechanism of that repression and the gene cascade that ensues. Solution Hfr strain means high frequency strain in which the plasmid of the bacteria integrates with the bacterial Genome so it is termed as high frequency, F- cells are the strain which doesn\'t consists of the F fertile factor, When the Hfr strains conjugated with F- strain the other genetic material other than f factor is transferred so that no change in the F- strains. Where in case of F+ the fertile factor will transfer it\'s genome so F- will turned into F+ cell..