.......... has been described as a tripartite ribbon like structure situated between pairing homologous chromosomes

Options

A. Synaptonemal complex
B. Lateral elements
C. Axial filaments
D. Central elements

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a structure that is described as a "tripartite ribbon-like structure" located between pairing homologous chromosomes.

2. **Identifying Key Terms**:
- **Tripartite**: This indicates that the structure is made up of three parts.
- **Ribbon-like structure**: This suggests a linear or elongated form.
- **Homologous chromosomes**: These are pairs of chromosomes, one inherited from each parent, that are similar in shape, size, and genetic content.

3. **Analyzing Options**:
- **Synaptonemal complex**: This is a protein structure that forms between homologous chromosomes during meiosis. It is known to facilitate chromosome pairing and recombination.
- **Lateral elements**: These are part of the synaptonemal complex but do not describe the entire structure.
- **Axial filaments**: These are associated with flagella in certain bacteria and are not relevant to the context of chromosomes.
- **Central elements**: These are also part of the synaptonemal complex but do not describe the entire structure.

4. **Connecting the Dots**: The synaptonemal complex is specifically known for its tripartite structure, consisting of two lateral elements and one central element. This fits the description in the question perfectly.

5. **Final Answer**: The structure that has been described as a tripartite ribbon-like structure situated between pairing homologous chromosomes is the **synaptonemal complex**.

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