Coupling and repulsion are the two faces of

Options

A. Crossing over
B. Linkage
C. Chiasmata
D. Mutation

Explanation

**Step-by-Step Solution:**

1. **Understanding Coupling and Repulsion:**
- Coupling refers to the arrangement where dominant alleles are located on the same homologous chromosome, while recessive alleles are on the other homologous chromosome. This is often referred to as the "Cis" configuration.
- Repulsion, on the other hand, occurs when each homologous chromosome carries one dominant and one recessive allele. This configuration is known as "Trans."

2. **Identifying the Context:**
- The question asks about the relationship between coupling and repulsion. Both terms are used to describe the arrangement of alleles on chromosomes and are important in genetics.

3. **Analyzing the Options:**
- **Option A: Crossing Over** - This involves the exchange of segments between non-sister chromatids of homologous chromosomes. This does not directly relate to coupling and repulsion.
- **Option B: Linkage** - This refers to genes that are located close to each other on the same chromosome and tend to be inherited together. Coupling and repulsion are indeed phases of linkage.
- **Option C: Chiasmata** - This is the point where two homologous non-sister chromatids exchange genetic material during crossing over, which is not directly related to coupling and repulsion.
- **Option D: Mutation** - This refers to changes in the DNA sequence and is unrelated to the concepts of coupling and repulsion.

4. **Conclusion:**
- After analyzing the options, it is clear that coupling and repulsion are two phases of linkage. Therefore, the correct answer is **Option B: Linkage**.

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