A trait that can be observed to occur or not to occur in an organism such as, for example, bacteria or plant(s). Genetic markers include such traits as: expression of luciferase in leaf cells (causing leaves to glow), resistance to specific antibiotics, the nature of the cell wall and capsule characteristics, requirements for a particular growth factor, and carbohydrate utilization, to mention a few. For example, if a culture of dividing (growing) bacteria that is not resistant to a particular antibiotic (i.e., lacks the trait of antibiotic resistance) is exposed to only the DNA isolated from bacteria that are resistant to the antibiotic, then a fraction of the cells exposed will directly incorporate this trait (some DNA) into their genome, hence acquiring the trait. The first genetically engineered plants bearing a marker gene were field tested in 1986.