Sub-species can be defined as:

Subspecies refer to populations of the same species that are geographically or ecologically distinct but still retain the ability to interbreed and produce viable, fertile offspring. This definition emphasizes the importance of both the genetic continuity within the subspecies and the differentiation that arises due to environmental factors or geographic barriers.

By focusing on the geographical distinction and the ability to produce fertile offspring, this definition captures the essence of how subspecies are recognized in biological taxonomy. It highlights that while subspecies may exhibit variations in traits (such as morphology, behavior, or adaptations to local environments), they are still fundamentally part of the same overarching species lineage.

The other choices illustrate different concepts in biology. While new species formation is crucial to evolutionary processes, it would not apply to subspecies, which are not separate species. The concept of organisms having no genetic relation pertains to completely different species or unrelated groups. Lastly, stating that a subspecies is a separate species with distinct traits contradicts the defining characteristics of subspecies since they must still be capable of interbreeding with members of the same species. Thus, the definition provided in the correct choice effectively captures the nuances of what constitutes a subspecies.