methods of Positive (direct) and negative (indirect) selection of mutants.
Positive selection involves the dection of mutant cells by the rejection of the unmutated parents cells. example- bacteria that have mutated and are resistant to penicillin will be identified when plated mutants will grow and form colonies. Parent cells cannot grow.
Negative selection - selects a cell that cannot perform a certain function using the techique of replica plating. A colony that grows on the plate with histidine cannot on the medium without is auxotrophic. (histidine requiring mutant). has a nutrient requirement absent in the parent.