A trisomic individual possesses extra -chromosomes :

Options

A. One extra chromosome
B. One less chromosome
C. Two extra chromosomes
D. One pair of extra chromosomes

Answer

**Step-by-Step Solution:**

1. **Understanding Trisomy**: Trisomy refers to a genetic condition where an individual has three copies of a particular chromosome instead of the normal two. This occurs due to a failure in chromosome segregation during cell division, specifically during gamete formation.

2. **Chromosome Count**: In humans, the normal diploid chromosome number is 46 (23 pairs). In a trisomic individual, there is an additional chromosome, leading to a total of 47 chromosomes. This can be represented as 2n + 1, where n is the haploid number (23).

3. **Example of Trisomy**: A well-known example of trisomy is Down syndrome, which is caused by an extra copy of chromosome 21. In this case, one gamete (egg or sperm) has an extra chromosome due to non-disjunction, leading to a fertilized egg with 47 chromosomes.

4. **Identifying the Extra Chromosome**: In the case of Down syndrome, the extra chromosome is specifically the 21st chromosome. Thus, a trisomic individual has one extra chromosome, which can be any of the chromosomes depending on the type of trisomy.

5. **Conclusion**: Therefore, a trisomic individual possesses one extra chromosome, resulting in a total of 47 chromosomes.

**Final Answer**: A trisomic individual possesses one extra chromosome.

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