Concepts of Genetics 11th Edition by William Klug,Michael Cummings,Charlotte Spencer,Michael Palladino

Exercise 3

Researching their family histories, a deaf couple learns that each of them has relatives through several generations who are deaf. With a rudimentary understanding of genetics, they also learn that one of many forms of deafness can be inherited as an autosomal recessive trait. They plan to have children, and based on the above information, they are concerned that some or all of their children may be deaf. To their delight, their first child has normal hearing. The couple turns to you as a geneticist to help explain this situation.
What conclusions could be drawn if their first child had been deaf?