Dear Javed, 

Its not compulsion to use only CT DNA. CT DNA mostly resembles with mamalian DNA structure thats why people are using it. Other main reason is its easy to extract from thymus gland of calf. CT dna can be extracted in more amount as its % is more in thymus gland only. people have used herring sperm DNA also for binding studies. 

Even you can use human blood gemomic DNA. Being easily available and easy correlation with mammalian DNA, CT DNA is widely used.  I hope this finds useful for you. 

Regards 

Poonam

 Mr. Ganaie,

Mainly due to the reasons which have been pointed out by Mrs/Miss Inamdar.  

 thank u  madamm...

At the same time, it's cheap in comparison to others.