Question

The point mutations ‘A to G’, ‘C to T’, ‘C to G’ and ‘T to A’ in DNA are called as
a. Transition, transition, transversion, and transversion respectively
b. Transition, transversion, transition and transversion respectively
c. Transversion, transversion, transition, and transition respectively
d. All four are transition

Answer 1

A point mutation is a mutation that affects only a single nucleotide of the nucleic acid. This type of mutation involves the substitution of one base for another. The term point mutation also includes deletions or insertions of a single base pair.

Complete answer:
- A point mutation is when there is an alteration in a single base pair.
- Point mutations can have one of three effects.
- First, a silent mutation, the base substitution, in which the altered codon corresponds to the same amino acid.
- Second, a missense mutation, the base substitution, where the altered codon corresponds to a different amino acid.
- Or third, nonsense mutation, the base substitution, where the altered codon corresponds to a stop signal.

Point mutations are of two types:

Transitions: This mutation occurs when pyrimidine bases are substituted with the pyrimidine bases or purine bases are substituted with the purine bases. For example, Adenine to Guanine (A to G) or Cytosine to Thymine (C to T).

Transversion: When a purine base is replaced by a pyrimidine base or pyrimidine base is replaced with a purine base, it is defined as a transverse type of mutation. For example, Adenine (A) to Thymine (T) and Guanine (G) to Cytosine (C).

Thus, A to G and C to T are transitions, and C to G and T to A are transversions.
Hence, the correct answer is option (A).

Note: The mutation is defined as an alteration in the base pair of a nucleotide sequence. Point mutation is when there is an alteration in a single base pair. In DNA, the complementary base of adenine is guanine and the complementary base of cytosine is thymine. When the point mutation occurs in between the purine- purine, and pyrimidine- pyrimidine, it is called transition and when a purine is exchanged with a pyrimidine or vice versa it is known as transversion.