## Core Concept
MELAS syndrome (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes) is a mitochondrial disorder. Mitochondrial disorders are inherited in a **maternal** pattern because only egg cells contribute mitochondria to the fertilized egg; sperm usually do not pass on their mitochondria during fertilization.

## Why the Correct Answer is Right
MELAS syndrome is caused by mutations in mitochondrial DNA. Since mitochondrial DNA is inherited solely from one's mother, the inheritance pattern of MELAS syndrome and other mitochondrial disorders is **maternal inheritance**. This means that all children of an affected mother will inherit the mutated mitochondrial DNA, but only the daughters will pass it on to their offspring.

## Why Each Wrong Option is Incorrect
* **Option A:** This option is incorrect because autosomal dominant inheritance involves a dominant allele that will cause the disorder if an individual has one copy of the allele. This does not apply to MELAS syndrome.
* **Option B:** This option is incorrect because autosomal recessive inheritance requires an individual to have two copies of the mutated allele (one from each parent) to express the disorder. MELAS syndrome does not follow this pattern.
* **Option C:** This option might seem plausible because X-linked inheritance involves genes on the X chromosome. However, MELAS syndrome is specifically related to mitochondrial DNA mutations, not nuclear DNA mutations on the X chromosome.

## Clinical Pearl / High-Yield Fact
A key point to remember is that in mitochondrial disorders like MELAS syndrome, the **severity and expression** can vary greatly among offspring due to the phenomenon of **heteroplasmy**. This is where a mixture of normal and mutated mitochondrial DNA coexists within the same cell or individual, influencing the severity of the disorder.

## Correct Answer: D. Maternal inheritance