What does it mean for a trait to be sex-linked?

When a trait is described as sex-linked, it means that the gene responsible for that trait is located on one of the sex chromosomes, which are the X and Y chromosomes in humans. This means that the inheritance of the trait is associated with the mechanisms of sex chromosome segregation during reproduction.

For example, because males have one X and one Y chromosome, they will inherit any X-linked traits from their mothers, while females have two X chromosomes, which means they can inherit X-linked traits from either parent. This location on the sex chromosomes can lead to different patterns of inheritance and expression between males and females, particularly for traits that are X-linked, such as color blindness or hemophilia.

Therefore, the defining factor of being sex-linked is the gene's location on a sex chromosome, which influences how and in what patterns that trait is passed on in a population.