What term describes the actual physical or behavioral characteristics of an organism?

The term that describes the actual physical or behavioral characteristics of an organism is phenotype. This concept encompasses all observable traits, including morphology, development, biochemical properties, physiology, and behavior, which result from the interaction between an organism's genetic makeup and its environment.

For instance, in animals, the phenotype would include traits such as fur color, ear shape, or behavior traits like aggression or sociability. Phenotype is distinct from genotype, which refers to the specific genetic makeup or the set of genes that an organism carries, including both dominant and recessive alleles.

Karyotype refers to the number and appearance of chromosomes in the nucleus of a cell, while allele describes one of the different forms of a gene that can exist at a specific locus on a chromosome. These terms relate to genetics but do not directly encompass the broader observable traits, thus distinguishing the relevance of phenotype in this context.