Diagnostic defined.
Diagnostic = characteristic of a particular species, genus, or phenomenon.
A diagnostic characteristic is a feature used to distinguish or identify a particular group of organisms. The feature is one that can be found in the majority of organisms that belong to a particular group (species, class, taxa, other). The characteristic must be present at some point during the organism’s lifetime, either in the embryonic stages or as an adult or both. This characteristic cannot be applied to organisms in other groups, thus excluding them from being in the specific group. For example, a diagnostic characteristic of amniote species is that they have an amniotic egg protected by the amniotic membrane. Only organisms in this group have this characteristic which makes it unique to the group.
The difference between diagnostic and a medical diagnosis is that a medical diagnosis’ purpose is to describe the cause or nature of a sickness or illness. A diagnostic characteristic is used more widely to describe an entire group. It is used to include the shared features of organisms that make them related (Aggarwal, 2015). The point of choosing diagnostic characteristics is to make it possible to recognize a unique clade.
Some diagnostic characteristics are easy to distinguish and are common knowledge such as all birds have feathers and all mammals have hair. These external characteristics make it easy to separate organisms into different groups. Examples of other diagnostic characteristics are the 5 chordate characteristics. These five characteristics include; a notochord, a dorsal hollow nerve cord, pharyngeal slits, a postanal tail, and an endostyle or thyroid gland. All chordates have these five characteristics at some point during their lives, including vertebrates.
There are 4 additional characteristics which make vertebrates unique from other chordates: possession of an endoskeleton, a cranium, a vertebral column, and neural crest cells.
Citations:
Aggarwal, Rohit, et al. “Distinctions Between Diagnostic and Classification Criteria?” Advances in Pediatrics., U.S. National Library of Medicine, July 2015, www.ncbi.nlm.nih.gov/pmc/articles/PMC4482786/.
Fishbeck, Dale W., and Aurora M. Sebastiani. Comparative Anatomy: Manual of Vertebrate Dissection. Morton Publishing, 2015.
