Meselson and Stahl Experiment

Scientists around the world are working to know about the genetic material

Then Griffith with his Transforming Principle changes the perspective.

Later on, it was proved that DNA is genetic material.

But now the discussion shifted from what is genetic material to how it replicates.

Or in simple words how DNA makes its multiple copies.

Now two scientists came to prove the replication of our genetic material

Firstly, Let us know briefly about the replication process.

An experiment was conducted in the year 1985.

It proved that DNA replication is semiconservative.

Which means that each parent DNA act as a template strand.

And the daughter DNA is formed.

Meselson and Stahl have done an experiment to prove this.

They use E.coli bacteria and isotope of nitrogen

The bacteria are grown in a culture medium containing (an isotope of nitrogen) using Cl.

As we all know DNA has nitrogenous bases so they contained instead of normal nitrogen.

This makes the DNa molecule denser and was separated by lighter DNA by centrifugation method.

Depending on the presence of and these fragments appear at a specific position due to the difference in density.

As DNA is denser so DNA appeared down the tube.

Now, the bacterial cells are allowed to grow on medium were washed and transferred to containing a medium.

Here an interesting thing happened

When the DNA was extracted from the first generation it was a hybrid.

Which means that one DNA strand was heavier () parental strand and a new one was lighter () (daughter strand).

In the second generation after 40 minutes contains an equal amount of hybrid and normal DNA.

In the third generation,25 % DNA were hybrid while 75 % were normal DNA molecules.

And hence proved DNA replicated through the semiconservative method.


Meselson and Stahl proved that DNA replicated through the semi-conservative method.

They used and inserted isotope of Nitrogen.

On division, the DNA of contained nitrogen in the first generation.

In the second and third generation, the percentage of hybrid DNA becomes 50% and 25% respectively.

The End