Achondroplasia is a form of dwarfism that is inherited in humans as an autosomal dominant disorder. A survey in a small country showed that, within a two-year period, there were 12 children with normal parents born with this disorder out of a total of 420,000 births. What is the mutation rate in mutations/locus/generation?
A) 1.4 × 10-5 B) 2.8 × 10-6 C) 2.5 × 10-5 D) 2.8 × 10-5 E) 7.4 × 10-6