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Class 12th Biology 2015 Set1 Delhi Board Paper Solution

Question 25

Explain the genetic basis of blood grouping in human population.


How did Hershey and Chase established that DNA is transferred from virus to bacteria?


In humans, the blood groups are controlled by a gene called gene 'I'. It has three alleles, namely IA, IB and i.

Table Showing the Genetic Basis of Blood Grouping in Human Population



Hershey and Chase worked on bacteriophages (viruses that infect bacteria).

When a bacteriophage infects a bacterium, the viral genetic material gets attached with the bacterial genetic material and then, bacteria treats the viral genetic material as its own to synthesise more viral particles.

Hershey and Chase worked to discover whether it was a protein or DNA that entered the bacteria from virus.

They labelled some phages with radioactive sulphur and the others with radioactive phosphorus.

These radioactive phages were used to infect E. coli.

Then, E.coli was blended and centrifuged to remove viral particles.

It was observed that bacteria with radioactive DNA were radioactive while those with radioactive proteins lost their radioactivity.

This showed that it is the DNA that enters the bacteria from viruses and not proteins. Hence, it was concluded that DNA is the genetic material.