**Core Concept**
Retinitis pigmentosa (RP) is a group of genetic disorders affecting the retina's ability to respond to light, leading to progressive vision loss. The disorder is caused by mutations in various genes responsible for photoreceptor cell function.

**Why the Correct Answer is Right**
The most common mode of inheritance for retinitis pigmentosa is autosomal dominant. This means that a single copy of the mutated gene is sufficient to cause the condition. In autosomal dominant inheritance, each child of an affected parent has a 50% chance of inheriting the mutated gene. The mutated genes responsible for RP often affect the function of photoreceptor cells, leading to the characteristic symptoms of night blindness, peripheral vision loss, and eventually, central vision loss.

**Why Each Wrong Option is Incorrect**
* **Option A:** Autosomal recessive inheritance is less common in RP, typically affecting individuals who inherit two copies of the mutated gene (one from each parent). This is not the most common mode of inheritance.
* **Option B:** X-linked inheritance is rare in RP, typically affecting males who inherit the mutated gene from their mothers. This is not the most common mode of inheritance.
* **Option C:** Mitochondrial inheritance is not a common mode of inheritance for RP, as the condition is primarily caused by nuclear gene mutations.

**Clinical Pearl / High-Yield Fact**
Retinitis pigmentosa is a genetically heterogeneous disorder, with over 70 genes associated with the condition. Understanding the mode of inheritance is crucial for genetic counseling and family planning.

**Correct Answer: A. Autosomal dominant**