What is a sex-linked trait?

A sex-linked trait is defined as a trait that is influenced by an allele located on the sex chromosomes, specifically the X or Y chromosomes. Since these chromosomes determine an individual's sex, traits that are linked to them can exhibit different patterns of inheritance compared to traits located on autosomes (non-sex chromosomes).

For example, in humans, certain conditions like hemophilia and color blindness are linked to genes on the X chromosome. Males, having only one X chromosome, will express these traits if they inherit the associated allele, while females, with two X chromosomes, may be carriers or express the trait depending on whether they inherit the allele on one or both X chromosomes. This highlights the unique patterns of inheritance observed in sex-linked traits, which can display different rates of expression in males versus females, depending on the genetic makeup inherited from their parents.

In contrast, traits that are influenced by multiple genes relate to polygenic inheritance and are not specific to the sex chromosomes, while traits that cannot be inherited do not conform to genetic inheritance principles. Non-genetic characteristics influenced by environmental factors are a distinct category that does not involve genetic influence at all, separating them from the genetic framework necessary for defining sex-linked traits.