Question

How might you provide evidence that DNA is the genetic material in mice? Design an experiment.

Answer 1

answer

• Evidences that proved DNA is the genetic material-

  Griffith used two strains of pneumococcus named Streptococcus pneumoniae, bacteria which infect mice .A type III-S (S-smooth) which was virulent.A type II-R (R-rough) strain which was nonvirulent.In the Griffth experiment, bacteria from the III-S strain were killed by application of heat, injected into mice-mice was killed.The injection of II-R strain didnot killed the mice alone but when their combination was added the mice developed a fatal infection and die.Griffith also isolated both live II-R and live III-S strains of pneumococcus from the blood of these dead mice.

  conclusion by griffth- the type II-R had been "transformed" into the lethal III-S strain by a' transforming principle' that would be the part of the dead III-S strain bacteria.

  2.The Avery-MacLeod-McCarty experiment was an experimental demonstration that showed DNA is the substance that causes bacterial transformation in the griffth's experiment.They found that when they pretreated the heat-killed S-strain with either a protease (that degrades proteins) or with DNAase that degrades DNA. Their idea was that if the transforming factor was a protein, then treatment of the heat-killed S-strain with a protease would destroy the protein and the transformation will be inhibited .Treatment with DNAase will have no effect on the transformation process.But if DNA were the genetic material, then the opposite would be true. In their experiments, Avery found that protease did not affect the ability of dead S-strain to transform into R strain but DNAase did.They concluded that the genetic material in transformation is most likely DNA.Thus DNA as a genetic material is concluded.

  3. The ability of the phages is to take over and control the metabolic aciivity of the bacteria to produce new phages.The radioactive labeling was done with S³⁵ and P.The protease and DNAases were added in the experimental tube.The proteases didnot had any effect on the transforming principle but DNAses did.Therefore DNA as a genetic material was confirmed.