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Conditional Probability - No Penetrance. |
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1. |
A certain genetics professor has brown hair and brown eyes.
His father and mother have brown hair and brown eyes. His sister and e of his
two brothers have brown hair and brown eyes. However, his other brother has blond
hair and blue eyes (how's that for a Mendelian family!). His wife has brown hair and blue eyes. Her three sisters and two brothers also have brown hair and blue eyes. Her four children by a previous marriage all had blue eyes but half of them had blond hair. You may assume that brown eyes (E) is dominant to blue eyes (e) and that brown hair (B) is dominant to blond hair (b) |
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a. |
What is the probability any child that they decide to have would have brown eyes? |
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b. |
What is the probability any child that they decide to have would have both blond hair and brown eyes? |
| 2. | Emmett was blue-green color deficient (a sex-linked, recessive trait). His daughter, Mildred, had normal color vision. Mildred's son, Fergus, had one sister and two brothers. Fergus and his brother Rick had normal color vision. His older brother Curtis had blue-green color deficiency. His sister Ann married a normal man with normal color vision. |
| What is the probability that Ann's son would have blue-green color-deficiency? | |
| 3. | A young couple, Susan and Bill, comes to you - a family physician - and tells you that they want to start a family but that they are very worried about having a child with cystic fibrosis. | |
| Cystic fibrosis is an autosomal recessive genetic disease affecting approximately 30,000 children and adults in the United States. One in 30 Caucasians (of mixed Northern European descent) is an unknowing, symptom-less carrier (heterozygote) of the defective gene. | ||
| The only information that you have is that both Susan and Bill are healthy and that they are Caucasians of mixed Northern European descent. | ||
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a. |
Based on this limited information, what is the probability that they will have a child with cystic fibrosis? | |
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b. |
After you tell the couple the probability from Part a, Susan tells you that while her parents are normal her brother Ted has cystic fibrosis. She wants to know how this would change the probability. What can you tell her? | |