24. The base analog 2-aminopurine pairs With thymine, and can occasionally pair with cytosine. The type of mutation induced by 2-aminopurine is
(1) transversion       (2) Transition.
(3) deletion             (4) nonsense.

The type of mutation induced by the base analog 2-aminopurine is a transition mutation.

Explanation of each option:

1. Transversion mutation: This occurs when a purine is replaced by a pyrimidine or vice versa. Since 2-aminopurine usually pairs with thymine (a pyrimidine) but can occasionally pair with cytosine (also a pyrimidine), the mutation caused is not a purine-pyrimidine switch, so transversion is incorrect.

2. Transition mutation: This is a substitution mutation where a purine is replaced by another purine or a pyrimidine is replaced by another pyrimidine. 2-aminopurine is an adenine (purine) analog that normally pairs with thymine but can mispair with cytosine, leading to an A-T to G-C base pair change, which is a purine to purine substitution, fitting the definition of a transition mutation.

3. Deletion mutation: This involves the loss of nucleotides and is unrelated to base analog-induced point mutations, so this is incorrect.

4. Nonsense mutation: This is a point mutation leading to a premature stop codon, causing early termination of protein synthesis. 2-aminopurine does not directly cause nonsense mutations, so this is incorrect.

Introduction:
2-Aminopurine is a base analog widely studied for its role in causing mutations during DNA replication. It primarily pairs with thymine but can occasionally pair with cytosine, leading to specific types of mutations. Understanding the mutation type induced by 2-aminopurine is crucial for genetics and molecular biology studies, especially for deciphering mutagenesis mechanisms.

2-Aminopurine (2-AP) is a base analog that mimics adenine, a purine base. It pairs normally with thymine (T) but can occasionally mispair with cytosine (C). This mispairing causes base substitutions in DNA, specifically A-T to G-C transitions, which are examples of transition mutations. A transition mutation involves the replacement of a purine with another purine (A ↔ G) or a pyrimidine with another pyrimidine (C ↔ T). Since 2-aminopurine is a purine analog and causes such purine-purine substitutions, it induces transition mutations.

Transversion mutations differ as they involve purine-pyrimidine swaps, which is not typical for 2-aminopurine. Deletions involve loss of base pairs rather than substitutions, and nonsense mutations cause premature stop codons, neither of which are directly induced by 2-aminopurine.

Hence, the correct answer is option (2) Transition mutation induced by 2-aminopurine due to its mispairing behavior with cytosine during DNA replication.