Purine-to-Purine DNA Base Substitution

Correct Answer: Transition

From the notes: Two types of nucleotide substitution mutations:

• Transition: Replacement of a purine by another PURINE (A↔G) OR replacement of a pyrimidine by another PYRIMIDINE (C↔T/U). The base TYPE remains the same. ✔
• Transversion: Replacement of a PURINE by a PYRIMIDINE or vice versa (e.g., A→C, G→T). The base TYPE changes.

Purines vs. Pyrimidines

• Purines: Adenine (A) and Guanine (G) — double-ring structures
• Pyrimidines: Cytosine (C), Thymine (T), Uracil (U) — single-ring structures

Other Mutation Processes (from notes — Q93 match)

• Transduction: Transfer of DNA from one bacterium to another by bacteriophage
• Conjugation: Genetic exchange between two living bacteria by direct contact
• Transformation: Direct uptake of exogenous genetic material by a bacterial cell