General:
* Traits
* Features
* Properties
* Attributes
* Qualities
* Aspects
* Elements
* Factors
More specific:
* Phenotype (referring to observable characteristics)
* Genotype (referring to genetic makeup)
* Morphology (referring to physical structure)
* Physiology (referring to bodily functions)
* Behavior (referring to actions and reactions)
The best word choice will depend on the specific context and the type of characteristics you are referring to.
