John and Sarah are contemplating having children, but both have a family history of Tay Sach's Disease, which is lethal usually by the age of 2 or 3 years. John had a brother die of Tay Sach's and Sarah's great grandparents (on her father's side) had a daughter die of the disease. All other members of the family are healthy. What is the probability that John and Sarah's first child will be affected with Tay Sachs?

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TaySachs disease is a recessive genetic disorder meaning a child needs two copies of the defective g... View the full answer