Due to the activity of recombinase enzyme, an X-shaped structure is observed between non-sister chromatids of homologous chromosomes. This is known as :-

Options

A. Diad
B. Bivalent
C. Synaptonemal complex
D. Chiasmata

Answer

To solve the question regarding the X-shaped structure observed between non-sister chromatids of homologous chromosomes due to the activity of the recombinase enzyme, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Chromosomes**:
- Homologous chromosomes are pairs of chromosomes that are similar in shape, size, and genetic content. Each chromosome in a pair consists of two sister chromatids.

2. **Identifying the Structure**:
- During meiosis, specifically in the pachytene stage of prophase I, homologous chromosomes pair up closely. This pairing is crucial for genetic recombination.

3. **Role of Recombinase Enzyme**:
- The recombinase enzyme facilitates the exchange of genetic material between non-sister chromatids of homologous chromosomes. This process is known as crossing over.

4. **Formation of Chiasmata**:
- The physical manifestation of this genetic exchange is the formation of an X-shaped structure called chiasmata. This structure indicates the points where chromatids have crossed over and exchanged segments of DNA.

5. **Differentiating Other Terms**:
- While dyad refers to a pair of homologous chromosomes, and bivalent refers to the pairing of two homologous chromosomes each consisting of two chromatids, the term synaptonemal complex refers to the protein structure that forms between homologous chromosomes during synapsis. However, the specific X-shaped structure formed due to crossing over is known as chiasmata.

6. **Conclusion**:
- Therefore, the correct answer to the question is that the X-shaped structure observed between non-sister chromatids of homologous chromosomes due to the activity of the recombinase enzyme is called **chiasmata**.

### Final Answer:
**Chiasmata**