The phenomenon of closely placed genes being inherited together is

Options

A. Linkage
B. Crossing over
C. Gene interaction
D. Qualitative inheritance

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the phenomenon where closely placed genes are inherited together. This relates to genetic inheritance patterns.

2. **Identifying Key Terms**: The terms provided in the options are:
- Linkage
- Crossing Over
- Gene Interaction
- Qualitative Inheritance

3. **Analyzing Linkage**:
- Linkage refers to genes that are located close to each other on the same chromosome.
- Because they are physically close, they tend to be inherited together during meiosis, which is the process of cell division that produces gametes.

4. **Understanding Independent Assortment**:
- According to Mendel's law of independent assortment, genes located on different chromosomes are inherited independently of one another.
- However, linked genes do not follow this rule because they are on the same chromosome and are inherited together.

5. **Crossing Over Explanation**:
- Crossing over is a process that occurs during meiosis where homologous chromosomes exchange segments of genetic material.
- While crossing over can affect the inheritance of linked genes, it does not define the phenomenon of genes being inherited together.

6. **Gene Interaction and Qualitative Inheritance**:
- Gene interaction refers to how the expression of one gene can be influenced by another gene, which is not relevant to the question.
- Qualitative inheritance involves traits controlled by a single gene, which again does not pertain to the inheritance of closely placed genes.

7. **Conclusion**: Based on the analysis, the correct answer is **linkage**, as it specifically describes the phenomenon of closely placed genes being inherited together.

**Final Answer**: The phenomenon of closely placed genes being inherited together is called **linkage**.

---