What term describes a unit of inheritance usually responsible for one trait?

The term that describes a unit of inheritance usually responsible for one trait is "gene." Genes are segments of DNA that encode instructions for making proteins, which ultimately influence various traits and characteristics of an organism. Each gene can affect a specific trait, such as flower color in plants or blood type in humans, and they are the basic physical and functional units of heredity passed from parents to offspring.

In contrast, chromosomes are structures within cells that organize and carry genes, but they encompass many genes and don’t represent a single unit of trait inheritance. DNA refers to the molecular structure that makes up genes and chromosomes, serving as the genetic material itself, but it is not the unit of inheritance in the sense of a distinct trait. RNA, although involved in protein synthesis and gene expression, is not a unit of inheritance; rather, it is a molecule that helps translate genetic information from DNA into proteins. Thus, the most accurate term for a unit of inheritance responsible for one trait is indeed a gene.