What are the characteristics of the DNA ladders used for gel electrophoresis?

The DNA ladder being used for gel electrophoresis should have these 5 characteristics:

1. The fragments within the ladder should be distinct and separable from each other.
2. The fragments in the ladder should exhibit stability over an extended period of time.
3. The concentration of each fragment should be sufficient for visualization after electrophoresis.
4. The ladder should undergo thorough purification to eliminate unnecessary and unidentified fragments, ensuring high purity.
5. The presence of loading dye in the ladder should not compromise the specificity of the DNA ladder.