This is a pattern of inheritance in which a gene for a particular trait or disorder is located on the X chromosome. Genes that are ‘recessive’ cause traits or conditions only when they are paired with a dominant gene. Genes usually come in pairs, except on the sex chromosomes in males. Males have one X chromosome that they inherit from their mothers and one Y chromosome that they inherit from their fathers. If a gene on the X chromosome causes a particular trait or disorder, a male will always show that trait or condition as they do not have another gene to cover up its effects. Females usually have a normal copy of that gene on their other X chromosome which covers up the effects of the recessive gene. Some common X-linked recessive disorders include hemophilia, Duchenne muscular dystrophy and color blindness.