Evidences of DNA as Hereditary Material (351)

Evidences of DNA as Hereditary Material (351)

Evidence of DNA as Hereditary Material:

Fred Griffith's Experiment:

        The first evidence of hereditary nature of DNA was provided by a British microbiologist Frederick Griffith by following experiment.

He was selected two varieties of bacteria.

1. Smooth with capsule and virulent i.e capable of producing disease.
2. Rough without capsule and non-virulent. 

When smooth virulent variety was introduced into mice, it died. When rough non-virulent variety injected into mice, it remained alive. Then Griffith changed the virulent smooth variety into non-virulent type by heat, when he introduced this changed variety in mice, it did not die. In the next experiment he injected both changed smooth variety and rough non-virulent variety together, the mice died surprisingly, although both varieties were non-virulent.

It was known by the research that rough non-virulent variety has gained some genetic property from smooth variety, which changed its genetic material. It was converted into virulent variety like smooth variety. This process is termed as transformation.

After 16 years, in 1944 Avery, Macleod and MaCarty confirmed the Griffith experiment. They performed many experiments on transformation. They discovered that only DNA has ability of transformation and not RNA.

Hershy and Chase Experiment:-

In 1952 Hershy and Chase proved that DNA performed the function of genetic material in Bacteriophage virus. Hershy and Chase labeled protein coat and DNA of Bacteriophage Sparately. Protein coat and DNA labeled with radioactive Sulphur and DNA with radioactive phosphorus. These two viruses used to attack bacterial cells. When these bacteria were checked, DNA with radioactive phosphorus was present in bacteria, whereas protein (outer capsule) was not found. It proved that DNA works as genetic material and it transmits from one generation to another.