**Core Concept**
Autosomal recessive diseases are genetic disorders caused by mutations in a single gene, inherited in an autosomal recessive pattern. This means that a person must inherit two copies of the mutated gene (one from each parent) to express the disease.

**Why the Correct Answer is Right**
Autosomal recessive diseases occur when a person inherits two copies of a mutated gene, one from each parent. The mutated gene disrupts the normal functioning of the protein, leading to the development of the disease. For example, sickle cell anemia is an autosomal recessive disease caused by a mutation in the HBB gene, which codes for hemoglobin. When both copies of the HBB gene are mutated, the individual produces abnormal hemoglobin, leading to the characteristic sickle-shaped red blood cells.

**Why Each Wrong Option is Incorrect**
**Option A:** Autosomal dominant diseases are caused by a mutation in one copy of the gene, whereas autosomal recessive diseases require two copies of the mutated gene to express the disease.
**Option B:** X-linked diseases are caused by mutations in genes on the X chromosome, which affects males more frequently due to their single X chromosome.
**Option C:** Mitochondrial diseases are caused by mutations in the mitochondrial DNA, which is inherited from the mother.

**Clinical Pearl / High-Yield Fact**
To remember the difference between autosomal recessive and autosomal dominant diseases, think of the "2" rule: autosomal recessive diseases require two copies of the mutated gene, while autosomal dominant diseases require only one copy.

**Correct Answer: C. Mitochondrial diseases are caused by mutations in the mitochondrial DNA, which is inherited from the mother.**