The mother has sickle cell disease; Father is normal; Chances of children having sickle cell disease and sickle cell trait respectively are:
**Core Concept**
Sickle cell disease is an autosomal recessive disorder caused by a mutation in the HBB gene, leading to abnormal hemoglobin production and characteristic sickle-shaped red blood cells. This question requires understanding of the genetic inheritance pattern of sickle cell disease.
**Why the Correct Answer is Right**
In autosomal recessive disorders, an individual must inherit two copies of the mutated gene (one from each parent) to express the disease. The mother, having sickle cell disease, is homozygous recessive (SS) for the mutated gene. The father, being normal, is either homozygous dominant (AA) or heterozygous (AS) for the gene. Since the father is normal, he is likely heterozygous (AS). When the mother (SS) and the father (AS) have children, each child has a 50% chance of inheriting the mutated gene from the father and a 50% chance of inheriting the normal gene. Therefore, each child has a 50% chance of having sickle cell disease (SS) and a 50% chance of having sickle cell trait (AS).
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it states a probability of 25% for sickle cell disease and 75% for sickle cell trait. This is not consistent with the expected inheritance pattern of an autosomal recessive disorder.
**Option B:** This option is incorrect because it states a probability of 75% for sickle cell disease and 25% for sickle cell trait. This is also not consistent with the expected inheritance pattern.
**Option C:** This option is incorrect because it does not provide a clear probability for either sickle cell disease or sickle cell trait.
**Clinical Pearl / High-Yield Fact**
In autosomal recessive disorders, the risk of transmitting the disease to offspring is 25% if the parent is heterozygous (carriers) and 100% if the parent is homozygous recessive (expresses the disease).
**Correct Answer:** C. 50% chance of sickle cell disease and 50% chance of sickle cell trait.