Question

Many scientists have contributed to the knowledge of genes, the structure of DNA, and how genes function. These people include

Hershey and Chase

Griffith

Rosalind Franklin

Meselsohn and Stahl

Barbara McClintock

Watson and Crick

Avery, McCarty, and MacLeod

Choose four from the list above and discuss their contributions to modern genetic theory.

PLEASE ANSWER THIS ASAP

Answer 1

Harshey and Chase:- They have used radioactive phosphorous and radioative sulphur tracers to show when the bacteriophage T2 infects its host cell, E.coli phosphorous containing DNA transfers genetic information not sulphur containing protein for viral replication.

Avery, McCarty and MacLeaod:- They have found that DNA extracted from a virulent strain of the bacterium streptococcus pneumoniae genetically transformed a non-virulent strain of this organism into a virulent form. So they have concluded that DNA extracted from virulent strain carrying inheritable genetic message for virulence.But there is doubt for other scientist that protein impurities were attached to this virulent strain then which is genetic material DNA or protein? But strain after treating with proteolytic enzymes showed genetic transformation but treating with nucleases they didnt show transformation.

Griffith Experment:- Griffith used R & S strain of S.pneumoniae. S strain showing mucous coat and R strain lack of it.These are injected into mice.

The one which was infected with the S strain developed pneumonia and died while that infected with the R strain stayed alive. In the second stage, Griffith heat-killed the S strain bacteria and injected into mice, but the mice stayed alive. Then, he mixed the heat-killed S and live R strains. This mixture was injected into mice and they died. In addition, he found living S strain bacteria in dead mice. From this experiment he concluded that some transforming priciple is present but he didnt identify which is that. But it is milestone of transforming principle.

Messelson and stahl experiment:- They have shown that semiconservative model of DNA replication. They have used nitrogen for this.