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

The correct term for a segment of DNA on a chromosome that codes for a specific trait is a gene. Genes are the basic units of heredity and carry the information necessary for the growth, development, and functioning of living organisms. They are composed of sequences of nucleotides, which determine the amino acid sequences in proteins, ultimately influencing an organism's traits and characteristics.

In contrast, the other terms have distinct meanings in genetics. A chromatid refers to one of the two identical halves of a replicated chromosome, which plays a role during cell division. An allele is a version of a gene that may vary between different individuals, contributing to genetic diversity. A locus refers to the specific physical location of a gene on a chromosome, not the gene itself. Understanding these distinctions helps clarify the functionality and structure of genetic material in relation to traits.