Problem: Sickle Cell Anemia (read more about sickle cell here http://science.edu

Question

Problem: Sickle Cell Anemia (read more about sickle cell here http://science.education.nih.gov/supplements/nih1/genetic/activities/activity2_database.htm)

Sean marries Crystal. Sean had a father with sickle cell anemia. Sadly, his father died from complications of his sickle cell anemia while at the hospital trying to recover from injuries from a car accident. Neither Sean nor his mother show any signs of sickle cell anemia. Because his father was known to have sickle cell anemia, Sean was able to deduce that his own genotype must be heterozygous. That is, he has sickle cell trait. Although neither of Crystal's parents suffered from sickle cell anemia, she knows it is in her family, and decided to be tested to see if she also has the heterozygous condition or not. The results came in...Crystal also has sickle cell trait. Knowing that they are both heterozygous, Sean and Crystal decided they should determine the probability of any one of their future children inheriting two copies of the sickle cell allele. If this happened, they know their child would suffer from sickle cell anemia, thus wanted to know the risks. Complete a Punnett square on your own paper to determine the chance of sickle cell anemia (not sickle cell trait) in a child between them. What is this chance?

0 (0%)

1/4 (25%)

1/2 (50%)

3/4 (75%)

Explanation / Answer

Probability of normal child with genotype HbA HbA = 1/4 = 25%

Probability of carrier child with genotype HbA HbS (heterozygous) = 1/2 = 50%

Probability of affected child with genotype HbS HbS = 1/4 = 25%.

Therefore, probability of child with sicke cell anemia is 25%. Option 2 is correct.

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