Question

During replication an error occurs resulting in mispairing between a T in the old strand of DNA and C in the new strand. Following a second round of replication, which type of base pair change mutation will result?

1. Transition
2. Deletion
3. Insertion
4. Transversion
5. Inversion

Answer 1

The correct option is D transversion

Before understanding why the correct option is Transversion let's first discuss about two types of nucleotides, these include

Purine:- Adenine , guanine

Pyrimidine:- Cytosine and Thymine

Now Transversions are the point mutations in which a purine is changed for a pyrimidine spontaneously. As per the question the new strand has C which is mismatched and in normal conditions it should have been A, because in parent strand the complementary base pair was T.

Now after second round of replicate the parent and new strand will seperate and replicate. Assuming no new mistmatching there ,the new strand's C will pair with G in daughter strand , but if the mistmatching was not done in the first case then instead of G you should have got T.

So you can see that T ( normal conditions ) have been changed to G ( due to mistmatching in first case) in second round of replication so there is pyrimidine to purine exchange hence the Transversion mutation is seen.