Question

What is the major difference between DNA and cDNA?
A. Exons absent in DNA
B. Introns absent in cDNA
C. Introns present in cDNA
D. Both (A) and (B)

Answer 1

DNA is the hereditary material of major groups of organisms present in the living world, consists of a double-helical structure made up of sugar-phosphate backbone and contains bases such as Adenine, Guanine, Cytosine, and Thymine. DNA is mainly present in the nucleus and the mitochondria of the cell coding for mRNA. cDNA is the double-stranded complement of the mRNA formed by reverse transcription.

Complete answer:
As the introns are spliced out from the pre-mRNA to form mRNA, the cDNA thus obtained from the reverse transcription of mRNA will be free of introns.
Hence option B is the correct answer.

Additional Information:
Introns are the nucleotide sequence that does not code for proteins and exons are the sequence that code for the protein and as a result the introns are removed from the mRNA during RNA splicing. The presence of introns and exons is seen in DNA.
Hence option A is incorrect.
The introns are spliced out of the pre-mRNA obtained from the DNA. The cDNA is obtained from the mRNA that does not contain an intron.
Hence the option C. is incorrect.
As option A is incorrect, option D is also incorrect.

Note:
cDNA refers to the complementary DNA synthesized mainly from the cytosolic mRNA. It is helpful in the expression of the eukaryotic gene in bacteria lacking an RNA splicing mechanism. The cDNA can be made only from the eukaryotic mRNA because the prokaryotic mRNA is found to be unstable. In the case of the human dystrophin gene, as much as 99% of the DNA sequence is composed of introns.