Sickle cell disease is an inherited blood disorder that affects red blood cells. Since it is a recessive disorder, a person inheriting two sickle cell genes will have the disease, whereas a person inheriting only one sickle cell gene will be healthy, but will carry the sickle cell trait. If both parents have the sickle cell trait, and it is equally likely whether a parent passes on the gene for sickle cell trait, determine the probability that
1. an offspring will have the disease .
2. an offspring will have the sickle cell trait.
3. an offspring will neither have sickle cell anemia not the sickle cell trait.
To determine the probability of each scenario, we need to use Punnett squares and understand the principles of genetics.
1. Probability that an offspring will have the disease:
In order for an offspring to have the disease, they must inherit two copies of the sickle cell gene (one from each parent). Both parents have the sickle cell trait, meaning they carry one copy of the sickle cell gene but do not have the disease.
Let's represent the trait as "S" for normal hemoglobin and "s" for sickle cell hemoglobin. Using a Punnett square, we can determine the outcomes:
| S | s |
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S | SS | Ss |
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s | Ss | ss |
There are four possible outcomes: SS, Ss, Ss, ss. Out of these, only one results in the offspring having the disease (ss). Therefore, the probability that an offspring will have the disease is 1 out of 4, or 1/4.
2. Probability that an offspring will have the sickle cell trait:
To have the sickle cell trait, an offspring needs to inherit one copy of the sickle cell gene from either parent (Ss). Again, using the Punnett square, we can determine the outcomes:
| S | s |
------------------
S | SS | Ss |
------------------
s | Ss | ss |
There are four possible outcomes: SS, Ss, Ss, ss. Three out of the four outcomes (SS, Ss, Ss) result in the offspring having the sickle cell trait. Therefore, the probability that an offspring will have the sickle cell trait is 3 out of 4, or 3/4.
3. Probability that an offspring will neither have sickle cell anemia nor the sickle cell trait:
For an offspring to have neither the disease nor the trait, they must inherit two normal hemoglobin genes (SS). Referring to the Punnett square:
| S | s |
------------------
S | SS | Ss |
------------------
s | Ss | ss |
There are four possible outcomes: SS, Ss, Ss, ss. Only one outcome (SS) results in the offspring neither having the disease nor the trait. Therefore, the probability that an offspring will have neither sickle cell anemia nor the sickle cell trait is 1 out of 4, or 1/4.
Use a Punnett Square.
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