The combined form of coupling and repulsion is -

Options

A. crossing over
B. mutation
C. linkage
D. disjunction

Answer

To solve the question, "The combined form of coupling and repulsion is -", we need to analyze the terms involved and their meanings in the context of genetics.

### Step-by-Step Solution:

1. **Understanding Coupling and Repulsion**:
- **Coupling** refers to the situation where two or more alleles are inherited together. This usually occurs when the alleles are located close to each other on the same chromosome.
- **Repulsion** refers to the situation where alleles are inherited separately, often because they are located on different chromosomes or are far apart on the same chromosome.

2. **Identifying the Combined Form**:
- The question asks for the combined form of these two concepts. In genetics, this is often related to how genes are inherited and how they can influence each other during processes like meiosis.

3. **Analyzing the Options**:
- **Crossing Over**: This is a process during meiosis where homologous chromosomes exchange genetic material. This can lead to new combinations of alleles.
- **Mutation**: This refers to changes in the DNA sequence, which can create new alleles but is not directly related to coupling and repulsion.
- **Linkage**: This refers to genes that are located close to each other on the same chromosome and tend to be inherited together (coupling).
- **Disjunction**: This is the separation of chromosomes during meiosis, which can lead to independent assortment of alleles.

4. **Conclusion**:
- The combined form of coupling (where alleles are inherited together) and repulsion (where alleles are inherited separately) is best represented by **crossing over**. This process allows for the mixing of alleles, leading to new combinations that can include both coupled and repelled alleles.

### Final Answer:
The combined form of coupling and repulsion is **crossing over**.

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