A man is heterozygous for the allele causing Huntington's disease. His wife does not have Huntington's disease, but her father did. What is the chance that their offspring will have the disease?

A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

The man is heterozygous for the allele causing Huntington's disease, which means he has one dominant allele and one recessive allele. His wife does not have the disease, but her father did, which means she is likely heterozygous for the allele or a carrier.

When the man and his wife have offspring, there is a 50% chance that their child will inherit the dominant disease-causing allele from the father and a 50% chance that they will inherit the normal allele from the mother. Therefore, there is a 50% chance that their offspring will have the disease.