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 need to understand what pedigree analysis is and the types of disorders it can evaluate.

### Step-by-Step Solution:

1. **Understand Pedigree Analysis**:
- Pedigree analysis is a method used to study the inheritance patterns of genetic disorders in families. It helps trace the presence of a gene through generations and determine whether a disorder is dominant, recessive, or linked to sex chromosomes.

**Hint**: Remember that pedigree charts are useful for tracking Mendelian (single-gene) disorders.

2. **Identify the Options**:
- The disorders listed are:
A. Cystic fibrosis
B. Down syndrome
C. Sickle cell anemia
D. Phenylketonuria

**Hint**: Look at each disorder and categorize them as Mendelian or chromosomal.

3. **Classify the Disorders**:
- **Cystic fibrosis**: A Mendelian disorder caused by mutations in the CFTR gene, inherited in an autosomal recessive manner.
- **Down syndrome**: A chromosomal disorder caused by trisomy of chromosome 21 (an extra chromosome).
- **Sickle cell anemia**: A Mendelian disorder caused by a mutation in the HBB gene, inherited in an autosomal recessive manner.
- **Phenylketonuria (PKU)**: A Mendelian disorder caused by a mutation in the PAH gene, inherited in an autosomal recessive manner.

**Hint**: Identify which of these disorders is related to chromosomal abnormalities rather than single-gene mutations.

4. **Determine Which Disorder Cannot Be Studied**:
- Since pedigree analysis is effective for Mendelian disorders, we can analyze cystic fibrosis, sickle cell anemia, and phenylketonuria using pedigree charts.
- However, Down syndrome, being a chromosomal disorder, cannot be effectively studied using pedigree analysis.

**Hint**: Chromosomal disorders typically involve larger structural changes in chromosomes that pedigree analysis cannot track effectively.

5. **Conclusion**:
- The disorder that cannot be studied by pedigree analysis is **Down syndrome**.

### Final Answer:
**Down syndrome** is the disorder that cannot be studied by pedigree analysis.