Which term best describes the physical expression of genetic traits?

The term that best describes the physical expression of genetic traits is "phenotype." The phenotype encompasses all observable characteristics of an organism, which include not just physical appearances such as height, eye color, and hair type, but also behavioral traits and physiological functions. These traits result from the interaction between an individual's genetic makeup and their environment.

In contrast, "genotype" refers to the genetic constitution of an individual, including the specific alleles inherited from their parents. While genotype provides the potential for various traits, it does not directly indicate how those traits will manifest physically.

"Allele" specifically refers to the different forms of a gene that can exist at a particular locus on a chromosome, thereby contributing to genetic variation but not capturing the complete picture of physical expression.

"Mutation" refers to a change in the DNA sequence that can lead to alterations in phenotype, but it is a specific occurrence rather than a term that describes the broad concept of physical traits as a whole.

Thus, phenotype is the comprehensive term that reflects how genetic information is expressed in an observable manner, which makes it the correct answer.