Which of the following disorders can’t be studied by pedigree analysis ?

Options

A. Cystic fibrosis
B. Down Syndrome
C. Sickle cell anemia
D. Phenylketonuria

Answer

To determine which disorder cannot be studied by pedigree analysis, we first need to understand what pedigree analysis is and how it relates to genetic disorders.

### Step-by-Step Solution:

1. **Understanding Pedigree Analysis**:
- Pedigree analysis is a method used to trace the inheritance of traits or disorders in families. It is particularly useful for studying Mendelian inheritance patterns.

**Hint**: Remember that pedigree analysis is most effective for disorders that follow Mendelian inheritance.

2. **Identifying Mendelian Disorders**:
- Disorders that can be studied through pedigree analysis typically show clear patterns of inheritance, such as autosomal dominant, autosomal recessive, or X-linked inheritance.

**Hint**: Look for disorders that are classified as Mendelian, as these can be traced in family trees.

3. **Evaluating the Options**:
- **Cystic Fibrosis**: This is an autosomal recessive disorder caused by mutations in the CFTR gene. It follows Mendelian inheritance.
- **Sickle Cell Anemia**: This is also an autosomal recessive disorder resulting from a mutation in the HBB gene on chromosome 11. It follows Mendelian inheritance.
- **Phenylketonuria (PKU)**: This is another autosomal recessive disorder caused by a deficiency of the enzyme phenylalanine hydroxylase. It follows Mendelian inheritance.
- **Down Syndrome**: This condition is caused by a chromosomal abnormality known as trisomy 21, where there is an extra copy of chromosome 21. This does not follow Mendelian inheritance patterns.

**Hint**: Identify which of the listed disorders is caused by a chromosomal abnormality rather than a genetic mutation.

4. **Conclusion**:
- Since Down Syndrome is a chromosomal abnormality and does not exhibit Mendelian inheritance, it cannot be effectively studied using pedigree analysis. The other three disorders (cystic fibrosis, sickle cell anemia, and phenylketonuria) can be studied using pedigree analysis.

**Final Answer**: The disorder that cannot be studied by pedigree analysis is **Down Syndrome**.