Achondroplasia is a common form of dwarfism caused by an autosomal dominant mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. Two copies of the mutant gene are invariably fatal before or shortly after birth. If a person with achondroplasia marries a person of normal height, what is the probability that both their first child and second child will have achondroplasia?
A. 1/8
B. 1/4
C. 1/2
D. 1
Answer: B