In: Biology
Using the rII mutant bacteriophage and E. coli strains B and K, semour benzer studied gene structure by both recombination and complementation. Wild type phages form plaques on strains B or K; rII forms plaques on B only.
A. In one set of experiments, Benzer infected E. coli strain B simultaneously with two different rII mutants. Progeny phages were collected and used to infect strain K, and, occasionally, plaques formed.
B. In a second set of experiments, Benzer infected strain K simultaneously with high amounts of two different rII mutant phages. Occasionally, plaques were observed from this infection.
Which set of experiments shows recombination, and which demonstrates complementation? briefly explain the difference
clear explanation please!
Experiment A shows recombination.
In this, Benzer combined E.coli strain B with two different rll mutants (phage chromosomes with mutations in 2 different rll genes). Hence a progeny from this cross produced new genotypes that are different from the parental genotypes. This is Recombination which represents new combinations of genes through the physical breakage and rejoining of chromosomes. Recombination uses multiple cycles of reinfection needed for plaque formation
Experiment B shows Complementation.
Experiment B is complementation. It does not need multiple cycles of reinfection for the plaque formation and infection. It does not involve any change in the genotypes of individual chromosomes; rather it represents the mixing of gene products.
Complementation occurs during the time that two (phage) chromosomes are in the same cell and can each supply a function. Afterward, each respective chromosome remains unaltered. When Benzer infected strain K with high amounts of two different rll mutants (phage chromosomes with mutations in different rll genes), complementation occurs in the same host (E.coli) cell. However, progeny that result from this complementation carry only the parental genotypes.
In complementation experiment, samples of the two phages to be tested are spread over a strip of host bacteria on a section of a petri plate at a high ratio of phages to bacteria to ensure that essentially every bacterium is infected with both phages. After a period of incubation, the growth or the absence of growth of the bacteria in the strip indicates whether the bacteria have lysed as a result of the phage infection.