Chapter 7, Problem 5P

Over a period of several years, a large hospital kept track of the number of births of babies displaying the trait achondroplasia. Achondroplasia is a very rare autosomal dominant condition resulting in dwarfism with abnormal body proportions. After 120,000 births, it was noted that 27 babies had been born with achondroplasia. One physician was interested in determining how many of these dwarf babies resulted from new mutations and whether the apparent mutation rate in this geographical area was higher than normal. He looked up the families of the 27 dwarf births and discovered that four of the dwarf babies had a dwarf parent. What is the apparent mutation rate of the achondroplasia gene in this population? Is it unusually high or low?