What characterizes a sex-linked trait?

A sex-linked trait is characterized by its association with genes located on the sex chromosomes, most commonly the X chromosome. This means that the expression of these traits is influenced by the sex of the individual. Females possess two X chromosomes (XX), while males have one X and one Y chromosome (XY). Because of this chromosomal arrangement, certain traits that are linked to genes on the X chromosome can manifest differently in males and females. For example, since males have only one X chromosome, any recessive allele present on that X can express the trait, while females may express the trait only if they have the allele on both of their X chromosomes.

This connection to sex chromosomes is what fundamentally distinguishes sex-linked traits from traits that are carried on autosomes (non-sex chromosomes), which are typically inherited in a Mendelian fashion and can be dominant or recessive regardless of the sex of the individual. Therefore, the key characteristic of sex-linked traits is their location on the sex chromosomes rather than being influenced solely by environmental factors, being dominant, or restricted to males only.