All genes on single chromosome forms :-

Answer

### Step-by-Step Solution:

1. **Understanding Genes on a Chromosome**:
- Genes are segments of DNA that code for proteins and determine traits. They are located on chromosomes, which are structures within cells that contain genetic material.

2. **Linkage Group Definition**:
- A linkage group is defined as a set of genes that are located on the same chromosome and tend to be inherited together. This is because they are physically close to each other on the chromosome.

3. **Independent Assortment**:
- During meiosis (the process of cell division that produces gametes), genes that are on the same chromosome do not assort independently. Instead, they are inherited together as a unit, which is a key characteristic of linkage groups.

4. **Phenomenon of Linkage**:
- The phenomenon where genes on the same chromosome are inherited together is known as linkage. This occurs because the genes are physically connected on the chromosome and are often passed on together during cell division.

5. **Crossing Over**:
- While genes on the same chromosome are typically inherited together, crossing over can occur during meiosis. This is when homologous chromosomes exchange segments of DNA. However, if the genes are very close to each other, the likelihood of crossing over occurring between them is reduced.

6. **Measuring Genetic Distance**:
- The distance between genes on a chromosome is measured in centimorgans (cM). One centimorgan corresponds to a 1% chance of recombination occurring between two genes during meiosis.

### Final Answer:
All genes on a single chromosome form a **linkage group**.

---