## **Core Concept**
The question tests understanding of Mendelian genetics, specifically the inheritance pattern of autosomal dominant disorders. In autosomal dominant inheritance, a single copy of the dominant allele is enough to cause the condition.

## **Why the Correct Answer is Right**
When one parent is an autosomal dominant heterozygote, they have one normal allele and one disease-causing allele. The possible genotypes of their offspring according to Mendelian laws are:
- 50% chance of inheriting the disease-causing allele (and thus expressing the disorder since it's dominant)
- 50% chance of inheriting the normal allele (and thus not expressing the disorder).
Therefore, there's a 50% chance that any given offspring will be affected.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests a 0% chance, which would be incorrect for an autosomal dominant condition because the heterozygous parent can pass the dominant allele to their offspring.
- **Option B:** This option suggests a 25% chance, which applies to autosomal recessive conditions when both parents are carriers, not to autosomal dominant conditions.
- **Option D:** This option suggests a 100% chance, which would only be true if the parent were homozygous for the dominant allele, not if they are heterozygous.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that autosomal dominant disorders can exhibit **variable expressivity** and **incomplete penetrance**, meaning the severity of the disorder can vary greatly between individuals, and some individuals with the disease-causing genotype may not display any symptoms at all.

## **Correct Answer:** . 50%