Consider the following disorders:
Colourbliness, Thanlassemia, Klinefelter's syndrome , Myotonic dystrophy, Sickle cell anaemia, Phenylketonuria, Turner's syndrome
How many of the above disorders are Mendelian autosomal disorders ?

Options

A. Six
B. Two
C. Five
D. Four

Answer

To determine how many of the listed disorders are Mendelian autosomal disorders, we need to analyze each disorder based on its genetic classification.

1. **Color Blindness**: This is a sex-linked disorder, specifically linked to the X chromosome. Therefore, it is **not** a Mendelian autosomal disorder.

2. **Thalassemia**: This is a genetic blood disorder caused by mutations in the genes responsible for hemoglobin production. It is classified as a Mendelian autosomal disorder.

3. **Klinefelter's Syndrome**: This is a chromosomal disorder caused by the presence of an extra X chromosome in males (XXY). Thus, it is **not** a Mendelian autosomal disorder.

4. **Myotonic Dystrophy**: This is a genetic disorder that affects muscle function and is caused by a mutation in the DMPK gene. It is classified as a Mendelian autosomal disorder.

5. **Sickle Cell Anemia**: This is a genetic disorder caused by a mutation in the HBB gene, which is located on chromosome 11. It is classified as a Mendelian autosomal disorder.

6. **Phenylketonuria (PKU)**: This is a metabolic disorder caused by a mutation in the PAH gene, which is located on chromosome 12. It is classified as a Mendelian autosomal disorder.

7. **Turner's Syndrome**: This is a chromosomal disorder that occurs in females when one of the X chromosomes is missing or partially missing (45,X). Therefore, it is **not** a Mendelian autosomal disorder.

Now, let's summarize the findings:
- **Mendelian Autosomal Disorders**:
- Thalassemia
- Myotonic Dystrophy
- Sickle Cell Anemia
- Phenylketonuria

Thus, there are **4 Mendelian autosomal disorders** in the list provided.

**Final Answer**: D4

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