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Case No 1  Cystic Fibrosis

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Bill and Amy got married and decided to have a baby.

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They knew that Bill had a great-grandfather who had died from Cystic Fibrosis. For a person to be affected, he or she has to inherit one copy of the gene from each parent. Amy does not remember if any of her ancestors had the disease. They thought that the risk would be low, since they are both young and healthy. When baby Joe was born, they discovered that he had the disease! Bill and Amy were very unhappy and confused. They did not know how to take care of the baby. A long rough road was ahead of them. They asked the doctor to test them to see if they carry the gene in their DNA. A nurse drew blood from their arms and sent the samples to a laboratory for testing.  The results came back within a week. Both Bill and Amy carry one copy of the gene. They wished they took the test before they decided to have a baby.

What do you think the test results were? Let’s say that the gene for Cystic Fibrosis is s.

bulletBoth Bill and Amy have one copy of the s gene
bulletOnly Bill has one copy of the s gene
bulletOnly Bill has two copies of the s gene
bulletBoth Bill and Amy have two copies of the s gene


What is the chance of Bill and Amy’s next child developing the disease?


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