Which of the following disorders is not caused by pleiotropic alleles

Options

A. Sickle cell anaemia
B. Cystic fibrosis
C. Phenylketonuria
D. Erythroblastosis foetails.

Answer

To determine which disorder is not caused by pleiotropic alleles, we will analyze each of the provided options one by one.

### Step-by-Step Solution:

1. **Understanding Pleiotropic Alleles**:
- Pleiotropic alleles are those that can affect multiple traits or characteristics due to the action of a single gene.

2. **Analyzing Sickle Cell Anemia**:
- Sickle cell anemia is caused by a mutation in the hemoglobin gene. This mutation leads to the production of abnormal hemoglobin, which causes red blood cells to become sickle-shaped. This shape change affects multiple systems in the body, leading to various symptoms such as pain, anemia, and increased risk of infections.
- **Conclusion**: Sickle cell anemia is caused by pleiotropic alleles.

3. **Analyzing Cystic Fibrosis**:
- Cystic fibrosis is caused by mutations in the CFTR gene, which affects the production of mucus in various organs, particularly the lungs and pancreas. The thick mucus leads to respiratory and digestive issues, showcasing multiple effects from a single gene mutation.
- **Conclusion**: Cystic fibrosis is caused by pleiotropic alleles.

4. **Analyzing Phenylketonuria (PKU)**:
- Phenylketonuria is caused by a mutation in the PAH gene, which leads to the inability to metabolize phenylalanine. This can result in a variety of health issues, including intellectual disability and other neurological problems, indicating multiple effects from one gene.
- **Conclusion**: Phenylketonuria is caused by pleiotropic alleles.

5. **Analyzing Erythroblastosis Fetalis**:
- Erythroblastosis fetalis occurs when an Rh-negative mother has a baby with an Rh-positive father. The mother's immune system may produce antibodies against the Rh factor, leading to hemolytic disease in the fetus. This condition is not caused by a single gene affecting multiple traits but rather by the incompatibility of blood types.
- **Conclusion**: Erythroblastosis fetalis is **not** caused by pleiotropic alleles.

### Final Answer:
The disorder that is not caused by pleiotropic alleles is **Erythroblastosis Fetalis**.

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