In pulsed field gel electrophoresis, what is the minimum number of bands that must differ between two organisms for them to be considered unrelated?

In pulsed field gel electrophoresis (PFGE), the resolution of DNA fragments allows for detailed analysis of the genetic differences between organisms. The practice of using PFGE is particularly important in distinguishing between strains of bacteria, especially in epidemiological studies.

To consider two organisms as unrelated, there must be enough genetic variation to indicate distinct genetic lineages or backgrounds. The presence of a minimum number of different bands indicates that there are significant differences in the DNA fragments being analyzed. In this context, the idea is that 6 bands represents a threshold of genetic divergence that suggests the organisms do not share a recent common ancestor.

Having fewer than this threshold of differing bands may suggest that the organisms are more closely related or could potentially be variations of the same strain. Contrarily, demonstrating 6 or more differing bands establishes a more definitive genetic distinction, making it unlikely that the two organisms share significant genetic material.

Therefore, the requirement of differing bands in PFGE is a quantitative measure of genetic diversity and distance, and a minimum of 6 bands is crucial to support the conclusion that the organisms in question are indeed unrelated.