Question: Achondroplasia is caused by an autosomal dominant mutation within the fibroblast growth factor receptor-3 (FGFR3) gene on the short arm of chromosome 4. Pooled records from several large hospitals in the United States revealed that among 1,422,000 live births over a 20 year period, the number of babies born with achondroplasia was 31. Among those 31 babies, 18 of them had at least one parent with achondroplasia, and the remaining babies were born to two unaffected parents. What is the spontaneous mutation rate for achondroplasia?