Sex-linked inheritance refers to the transmission of traits or disorders that are influenced by genes carried on the sex chromosomes. In humans, the term often refers to traits or disorders influenced by genes on the X chromosome, as it contains many more genes than the smaller Y chromosome. Males, who have only a single copy of the X chromosome, are more likely to be affected by a sex-linked disorder than females, who have two copies. In females, the presence of a second, non-mutated copy may cause different, milder, or no symptoms of a sex-linked disorder.

There are two types of sex-linked inheritance: X-linked and Y-linked inheritance. X-linked inheritance is more common and occurs when a gene is present on the X chromosome but not on the Y chromosome. X-linked genes have distinctive inheritance patterns because they are present in different numbers in females (XX) and males (XY) . X-linked human genetic disorders are much more common in males than in females due to the X-linked inheritance pattern. Y-linked inheritance occurs when the mutated gene is present in the Y chromosome, which is present in males only.

Examples of X-linked recessive inheritance include color blindness, hemophilia A and B, and Duchenne muscular dystrophy. In X-linked dominant inheritance, one abnormal gene on the X chromosome can cause a sex-linked dominant disease. An example of X-linked dominant inheritance is Incontinentia pigmenti.