Young: Medical Genetics 
Multiple Choice QuestionsYoung: Medical Genetics
Example 2 with exercise
The parents of a child with severe sensorineural hearing loss are referred to the genetics clinic. They indicate that they have had three children: a son, a daughter and then another son, and that it is their daughter who was found at the age of 9 months to have severe hearing loss. The father of these children has two sisters both of whom have two sons. His parents are both well. No-one in his family has ever had a child with hearing loss before. The mother of the three children has a brother who has one son and one daughter. Her parents are also well and once again there is no known history of severe hearing loss in childhood. However, her maternal grandfather developed moderate hearing loss in his sixties. On specific questioning the mother recalls that her maternal grandmother was the sister of her husband’s paternal grandmother.
Now draw up the family tree. What is the most likely genetic explanation for the daughter’s severe hearing loss?
Once you have drawn up your family tree check your answer.
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