Consider the following statements : ​ 1. Adenoviruses have single-stranded DNA genomes whereas retroviruses have double-stranded DNA genomes. ​ 2. Common cold is sometime caused by an adenovirus whereas AIDS is caused by a retrovirus. ​ Which of the statements given above is/are correct? ​

Statement 2 is correct. Some adenovirus types (such as types 1, 2 and 5) cause upper respiratory infections, and adenoviruses are among the recognised causes of the common cold, though rhinoviruses cause most colds. AIDS is caused by HIV, a retrovirus that uses reverse transcriptase to copy its RNA into DNA.

Statement 1 is wrong, and this is where the question is really tested. Adenoviruses have a linear double-stranded DNA genome. Retroviruses carry a single-stranded RNA genome, present as two copies, which is later converted into DNA after entry. The statement has simply swapped the two genomes.

Option A fails because statement 1 is false. Option C fails for the same reason, and option D fails because statement 2 is true. Only option B fits.

Concept: virus classification by genome type (DNA or RNA, single or double stranded) and replication strategy. This matters for Mains GS-III on emerging diseases and vaccine design, since genome type decides which antiviral targets and vaccine platforms are possible.

Trap: Students remember that retroviruses involve reverse transcription, which makes DNA, and wrongly mark statement 1 as correct. The DNA is made from the RNA genome, so the genome itself is RNA.