The genetic disoders in which the patients have one chromosome less than normal humans are :

Options

A. Down's syndrome
B. Alpha Thalassemia
C. Turner's syndrome
D. Klinefeter's syndrome

Answer

To solve the question regarding genetic disorders where patients have one chromosome less than normal humans, we will analyze each option provided in the question step by step.

### Step 1: Understanding Normal Chromosome Count
Normal humans have a total of 46 chromosomes, arranged in 23 pairs. Any condition that results in having one chromosome less than this total would mean the individual has 45 chromosomes.

### Step 2: Analyzing Each Disorder
1. **Down's Syndrome**:
- This condition is caused by the presence of an extra copy of chromosome 21, leading to a total of 47 chromosomes (Trisomy 21).
- **Conclusion**: This disorder does not meet the criteria of having one chromosome less. **(Not the answer)**

2. **Alpha Thalassemia**:
- This is a blood disorder characterized by reduced levels of hemoglobin. It is not primarily a chromosomal disorder but rather a genetic mutation affecting hemoglobin production.
- **Conclusion**: This disorder does not involve a change in chromosome number. **(Not the answer)**

3. **Turner's Syndrome**:
- This disorder occurs due to the absence of one of the X chromosomes in females, resulting in a total of 45 chromosomes (45, X).
- **Conclusion**: This disorder fits the criteria of having one chromosome less than normal. **(This is the correct answer)**

4. **Klinefelter Syndrome**:
- This condition is characterized by the presence of an extra X chromosome in males, leading to a total of 47 chromosomes (47, XXY).
- **Conclusion**: This disorder also does not meet the criteria of having one chromosome less. **(Not the answer)**

### Final Answer
The genetic disorder in which the patients have one chromosome less than normal humans is **Turner's syndrome**.

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