Question

What is heriditary material? Prove idenlity of DNA as a genetic material.​

Answer 1

Chromosomes are made up of nucleic acids and proteins and are known as hereditary vehicles. In the first instance it appeared that proteins would be hereditary material, until experiments were performed to prove that nucleic acids act as genetic material.

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Much earlier, scientists believed that the genetic material was protein. In 1952, Hershey & Chase were the ones to conclusively prove that DNA is the genetic material. They worked with bacteriophages – viruses that infect bacteria. A bacteriophage attaches and delivers its genetic material into a bacterial cell, where it generates more virus particles. Hersey & Chase used bacteriophages to experiment as follows:

$\bold{\huge{\red{Labelling}}}$

Some viruses were grown on a medium containing radioactive phosphorus and some on a medium with radioactive sulfur.

$\bold{\huge{\red{Viruses}}}$

grown on radioactive phosphorus have radioactive DNA but not protein since DNA contains phosphorus but protein does not. Contrarily, viruses grown on radioactive sulfur have radioactive protein but not DNA since DNA does not contain sulfur.

$\bold{\huge{\red{Infection}}}$The radioactive phages were then allowed to infect the bacteria – E. coli.

$\bold{\red{Blending \: and \: Centrifugation}}$

As the infection progressed, the viral coats were removed from the bacteria by blending. Then, centrifugation was used to separate the viral particles from the bacteria.

$\bold{\huge{\red{Observation}}}$

Bacteria infected with viruses that have radioactive DNA, were radioactive, while bacteria infected with viruses that have radioactive protein, were not radioactive.

$\bold{\huge{\red{Conclusion}}}$

This experiment conclusively showed that DNA is the genetic material transferred from virus to bacteria, and not protein.

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