Sex-linked traits are characteristics that are associated with genes located on the sex chromosomes, primarily the X and Y chromosomes. In humans, males have one X and one Y chromosome, while females have two X chromosomes. This difference in chromosome composition means that certain traits, such as color blindness or hemophilia, are more likely to be expressed in males, as they have only one copy of the X chromosome. When a gene for a trait is located on the X chromosome, females can be carriers if they have one normal and one affected X chromosome. However, males will express the trait if their single X chromosome carries the gene for it. This pattern of inheritance explains why some traits are more common in one sex than the other.