This experiment was performed to determine the reversion rate and the recombination rate of the mutant phages, rII 29 and rII 31, when infected by E. Coli B and E. Coli K bacterial cells. Reversion rate is when the mutant gene will turn back to the wild type spontaneously (Biology Dept.), and recombination rates is when there is a cross over between the gene so that it turns back to the wild type gene (Biology Dept.) The wild type recombinant was determined by the phenotype from the parental phages based of the plaques on E. Coli K plates, which showed the reversion of the mutant phages that turned into wild type phages (Biology Dept.). The reversion rate for mutant rII 29 when infected with the two different bacterial cells was 5.88x10-4phage/ml