What is a segment of DNA on a chromosome that codes for a specific trait called?

A segment of DNA on a chromosome that codes for a specific trait is called a gene. Genes are the fundamental units of heredity and are responsible for the physical and biochemical traits observed in organisms. Each gene has a specific location on a chromosome, and it contains the instructions for synthesizing proteins that perform various functions in the cell.

While alleles refer to different versions of a gene that may produce variations in a given trait, they are not the entire segment of DNA itself but rather specific forms of a gene that can lead to differences in traits. Chromatids, on the other hand, are the two identical halves of a duplicated chromosome, and the genome encompasses the complete set of an organism's DNA, including all of its genes. Hence, the term "gene" most appropriately describes the DNA segment that codes for a specific trait.