Aneuploidy which results in loss of a complete homologous pair of chromosomes is

Options

A. Trisomy
B. Tetrasomy
C. Nullisomy
D. Euploidy

Answer

To solve the question regarding aneuploidy that results in the loss of a complete homologous pair of chromosomes, we will analyze the provided options step by step.

### Step-by-Step Solution:

1. **Understanding the Terms:**
- **Aneuploidy:** Refers to the presence of an abnormal number of chromosomes in a cell. This can involve either the gain or loss of chromosomes.
- **Homologous Pair:** A pair of chromosomes, one from each parent, that are similar in shape, size, and genetic content.

2. **Analyzing Each Option:**
- **Trisomy:** This condition involves the gain of an extra chromosome, resulting in a total of 2n + 1 chromosomes. Therefore, this option does not represent a loss of chromosomes.
- **Tetrasomy:** This condition involves the gain of two extra chromosomes, resulting in a total of 2n + 2 chromosomes. Similar to trisomy, this option also does not indicate a loss of chromosomes.
- **Nullisomy:** This condition refers to the loss of a complete homologous pair of chromosomes, resulting in a total of 2n - 2 chromosomes. This aligns with the question's requirement for the loss of a complete homologous pair.
- **Euploidy:** This term refers to a condition where there is a loss or gain of one or more complete sets of chromosomes (not just a pair). This does not specifically indicate the loss of a single homologous pair.

3. **Conclusion:**
- The correct answer is **Nullisomy**, as it specifically describes the loss of a complete homologous pair of chromosomes.

### Final Answer:
**Nullisomy** is the type of aneuploidy that results in the loss of a complete homologous pair of chromosomes.

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