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Options

A. a - recombination, b - crossing over
B. a - recombination, b - linkage
C. a - linkage, b - recombination
D. a - linkage, b - mutation

Answer

To solve the question regarding the physical association between two genes, we can break it down into a few steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the term that describes the physical association between two genes. This means we are looking for a concept in genetics that explains how genes are located close to each other on a chromosome.

2. **Identifying Key Terms**: The key terms in the question are "physical association" and "genes." In genetics, when two genes are located close to each other on the same chromosome, they tend to be inherited together.

3. **Recalling Genetic Concepts**: The term that describes the physical association of genes is known as "linkage." Linkage refers to the tendency of genes that are located close to each other on a chromosome to be inherited together during meiosis.

4. **Considering Other Options**: The question also mentions "recombination." Recombination refers to the process that generates new combinations of alleles (gene variants) during meiosis, but it is not the term that describes the physical association of genes.

5. **Final Answer**: Therefore, the correct answer to the question is "linkage."