**Core Concept**
Non-Mendelian inheritance refers to patterns of genetic inheritance that do not follow the simple Mendelian laws of segregation and independent assortment. These patterns arise due to various factors, including genetic mutations, chromosomal abnormalities, and interactions between genes.

**Why the Correct Answer is Right**
Mitochondrial inheritance is a classic example of non-Mendelian inheritance. Mitochondrial DNA is inherited solely from the mother, as only egg cells contribute mitochondria to the fertilized egg. This means that mitochondrial diseases and traits are passed down through the maternal lineage, defying the Mendelian laws of inheritance. Additionally, mitochondrial mutations can be inherited in a pattern known as heteroplasmy, where a mixture of normal and mutated mitochondrial DNA is present in cells, leading to variable expression of the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Autosomal dominant inheritance is a Mendelian pattern of inheritance, where a single copy of the dominant allele is sufficient to cause the disease. It does not represent non-Mendelian inheritance.
**Option B:** X-linked recessive inheritance is another Mendelian pattern, where the disease is more common in males, who have only one X chromosome. While it follows Mendelian laws, it is distinct from non-Mendelian inheritance.
**Option C:** Polygenic inheritance refers to the combined effect of multiple genes on a trait, but it still follows the principles of Mendelian inheritance. It does not represent non-Mendelian inheritance.

**Clinical Pearl / High-Yield Fact**
Remember that mitochondrial diseases can present with a wide range of symptoms, including muscle weakness, neurological disorders, and cardiac dysfunction. A key clinical clue is the presence of affected individuals in multiple generations, often with a maternal history of the disease.

**Correct Answer:** C. Mitochondrial inheritance.