The points at which crossing over has taken place between homologous chromosomes are called
(a) Protein axis
(b) Synaptonemal complexes
(c) Chiasmata
(d) Centromeres

Options

A. Protein axis
B. Synaptonemal complexes
C. Chiasmata
D. Centromeres

Answer

To solve the question regarding the points at which crossing over has taken place between homologous chromosomes, we will analyze the options provided and identify the correct terminology.

### Step-by-Step Solution:

1. **Understanding Homologous Chromosomes**:
- Homologous chromosomes are pairs of chromosomes (one from each parent) that are similar in shape, size, and genetic content. They consist of non-sister chromatids.

2. **Crossing Over**:
- Crossing over is a process that occurs during meiosis, specifically in prophase I, where homologous chromosomes exchange segments of genetic material. This process increases genetic diversity.

3. **Identifying the Relevant Stage**:
- The specific stage in meiosis where crossing over occurs is known as the diplotene stage of prophase I. During this stage, the homologous chromosomes are closely aligned and can exchange genetic material.

4. **Formation of Chiasmata**:
- The points at which the exchange of genetic material occurs are referred to as chiasmata. These are X-shaped structures that form between non-sister chromatids of homologous chromosomes during crossing over.

5. **Analyzing the Options**:
- (a) Protein axis: This is not related to crossing over.
- (b) Synaptonemal complexes: This refers to the structure that forms during the pairing of homologous chromosomes, but it is not the point of crossing over.
- (c) Chiasmata: This is the correct answer, as it specifically refers to the points where crossing over occurs.
- (d) Centromeres: These are the points of attachment for sister chromatids and are not related to crossing over.

6. **Conclusion**:
- The correct answer is (c) Chiasmata, as these are the points at which crossing over has taken place between homologous chromosomes.

### Final Answer:
(c) Chiasmata