**Core Concept**
Transition mutations are a type of point mutation that involves the substitution of one purine base for another (A for G) or one pyrimidine base for another (C for T) in DNA. This occurs due to the similar chemical structure of the bases involved in the substitution.

**Why the Correct Answer is Right**
Transition mutations are often caused by errors during DNA replication, where the correct base is incorrectly incorporated into the new DNA strand. This can occur due to the misalignment of the base pairing during replication, leading to the incorporation of a different base. Transition mutations can also occur due to the spontaneous deamination of cytosine to uracil, which can then be replaced by adenine during DNA replication.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because transversion mutations involve the substitution of a purine base for a pyrimidine base or vice versa, which is not the case for transition mutations.

**Option B:** This option is incorrect because frameshift mutations involve the insertion or deletion of nucleotides, which can alter the reading frame of the genetic code, whereas transition mutations involve the substitution of one base for another without affecting the reading frame.

**Option C:** This option is incorrect because point mutations can refer to any type of mutation that involves the substitution, insertion, or deletion of a single nucleotide, whereas transition mutations specifically refer to the substitution of one purine base for another or one pyrimidine base for another.

**Option D:** This option is incorrect because gene conversion involves the exchange of genetic material between homologous chromosomes, which is not related to the substitution of one base for another.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that transition mutations can be caused by errors during DNA replication, which can occur due to various factors such as age, exposure to mutagenic agents, or errors in DNA repair mechanisms.

**Correct Answer: C. Point mutations.**