In genetics, the term used to refer to the observable expression of a trait is?

The term that refers to the observable expression of a trait is "phenotype." Phenotype encompasses all the observable characteristics of an organism, including physical attributes like height, eye color, and behavior traits, which result from the interaction between the organism's genetic makeup and the environment.

Understanding phenotype is crucial in genetics because it allows scientists to study how specific traits manifest in individuals and populations. For example, breeding experiments can determine how certain phenotypes are passed down from one generation to the next and can also reveal the impact of environmental factors on genetic expression.

In contrast, an allele refers to the different versions of a gene that can exist, while genotype refers to the genetic constitution of an individual—specifically the alleles that an individual carries. The term "trait" is broader and can refer to any characteristic, not necessarily observable. Thus, "phenotype" specifically highlights the observable aspect of a trait, making it the most accurate term for the question.