## **Core Concept**
Autosomal dominant disorders are genetic conditions caused by mutations in one of the two copies of a gene. A single copy of the mutated gene is sufficient to cause the condition. These disorders are characterized by a dominant pattern of inheritance, meaning a single copy of the mutated gene will cause the condition, and each child of an affected parent has a 50% chance of inheriting the mutated gene.

## **Why the Correct Answer is Right**
The correct answer, **C. Huntington's disease**, is an autosomal dominant disorder. It is caused by an expansion of a CAG repeat in the Huntingtin gene on chromosome 4. This condition leads to progressive damage to the brain, affecting movement, cognition, and psychiatric stability. Because it is autosomal dominant, a mutation in one of the two copies of the gene is sufficient to cause the condition.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Cystic Fibrosis is an autosomal recessive disorder, not autosomal dominant. It is caused by mutations in the CFTR gene on chromosome 7, and a person must inherit two defective copies (one from each parent) to express the condition.
- **Option B:** Thalassemia major is also an autosomal recessive disorder. It results from mutations in the HBA1/2 or HBB genes, which are responsible for hemoglobin production. A person needs to inherit two mutated copies (one from each parent) to have the condition.
- **Option D:** Glycogen storage diseases are generally inherited in an autosomal recessive pattern. These diseases result from deficiencies in enzymes needed for glycogen synthesis or breakdown. Affected individuals usually inherit one defective gene from each parent.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl for autosomal dominant disorders like Huntington's disease is that **each child of an affected parent has a 50% chance of inheriting the mutated gene**, regardless of the child's sex. This pattern can help in genetic counseling for families with a history of such disorders.

## **Correct Answer: C. Huntington's disease**