The condition of an extra chromosome in addition to its homologous pair is

Options

A. (a) Trisomy
B. (b) Monosomy
C. (c) Polyploidy
D. (d) Nullisomy

Answer

To solve the question, "The condition of an extra chromosome in addition to its homologous pair is," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Chromosome Numbers**:
- In humans, the normal chromosome number is represented as 2n, where n is the number of homologous pairs. For humans, n = 23, so 2n = 46 chromosomes.

2. **Identifying the Condition of Extra Chromosome**:
- When there is an extra chromosome in addition to the normal homologous pair, the total number of chromosomes becomes 2n + 1. This means there are 47 chromosomes instead of the normal 46.

3. **Defining Trisomy**:
- The condition where there is one extra chromosome is specifically referred to as "trisomy." This term comes from the prefix "tri," meaning three, indicating that one of the chromosome pairs has three copies instead of the usual two.

4. **Eliminating Other Options**:
- **Monosomy**: This condition indicates that one chromosome is missing from the pair, represented as 2n - 1.
- **Polyploidy**: This refers to having multiple sets of chromosomes (e.g., 3n, 4n), which is not the case here.
- **Nullisomy**: This condition indicates that two chromosomes are missing from the set, represented as 2n - 2.

5. **Conclusion**:
- Since the question specifically asks for the condition of having an extra chromosome, the correct answer is "trisomy," which is represented as 2n + 1.

### Final Answer:
The condition of an extra chromosome in addition to its homologous pair is called **trisomy**.

---