X-linked traits are sex-linked traits determined by genes on the X-chromosome. Some X-linked traits in humans are; red-green colorblindness, Duchenne muscular dystrophy, hemophilia A, and hemophilia B. These are all recessive traits, and affect males with a much greater frequency than females.
There are also Y-linked traits on the Y-chromosome that are passed exclusively from father to son. One of these genes is the #"SRY"# gene called the "sex determination region Y gene." It controls the development of the male sex characteristics in a developing male fetus.