Young: Medical Genetics 
Multiple Choice QuestionsYoung: Medical Genetics
Example 3 with exercise
A family is referred in which the parents have two children: one son and one daughter, both of whom have unexplained muscle weakness. The parents are themselves healthy with no known muscle problems. The father has one brother and one sister who are both well, as are his parents. His brother has two healthy daughters. The mother has one brother and one sister, each of whom has one son and one daughter. Her brother has longstanding muscle weakness but both of his children are unaffected. Her sister has mild muscle weakness and both of her children are affected. The only other point to emerge in the family is that the mother had a maternal uncle who died in his thirties with ill defined neurological problems, attributed at the time to a diagnosis of ‘multiple sclerosis’. This uncle had two children, one boy and one girl, both of whom are reported to be entirely healthy. The parents are not aware of any possible blood relationship ancestors and do not know of any other relatives who have had neurological or muscle problems.
On the basis of this information draw up a family tree and speculate on the possible underlying inheritance pattern.
Once you have drawn up your family tree check your answer.
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