In the listed Medielian disorders, how many concerned with defective haemoglobin ?
Haemophilia, Cystic fibrosis, Sickel- cell anemia, thalaasemia, Phenylketonuria, Colour- blindness

Options

A. Two
B. One
C. Three
D. Four

Answer

To determine how many of the listed Mendelian disorders are concerned with defective hemoglobin, we will analyze each disorder one by one.

### Step-by-Step Solution:

1. **Identify the Disorders**: The listed disorders are:
- Hemophilia
- Cystic fibrosis
- Sickle-cell anemia
- Thalassemia
- Phenylketonuria
- Color blindness

2. **Analyze Each Disorder**:
- **Hemophilia**: This is a blood disorder related to the absence of clotting factors (e.g., factor VIII). It does not involve hemoglobin.
- **Cystic Fibrosis**: This is a genetic disorder that affects the lungs and digestive system. It is not related to hemoglobin.
- **Sickle-cell Anemia**: This is an autosomal recessive disorder caused by a mutation in the hemoglobin gene, leading to the production of abnormal hemoglobin (HbS). This disorder is directly related to defective hemoglobin.
- **Thalassemia**: This is also a genetic disorder that affects the production of hemoglobin. It can lead to reduced or absent production of one of the globin chains of hemoglobin, making it related to defective hemoglobin.
- **Phenylketonuria (PKU)**: This is a metabolic disorder caused by the absence of the enzyme phenylalanine hydroxylase. It does not involve hemoglobin.
- **Color Blindness**: This is a genetic condition affecting vision and is not related to hemoglobin.

3. **Count the Disorders Related to Defective Hemoglobin**: From our analysis, we find that:
- Sickle-cell anemia (1)
- Thalassemia (2)

Thus, there are **2 disorders** that are concerned with defective hemoglobin.

### Final Answer:
**2 disorders (Sickle-cell anemia and Thalassemia) are concerned with defective hemoglobin.**

---