*5.1.3 X-linked recessive*

X-linked recessive inheritance pattern is caused by a mutation in a gene situated on the X chromosome. Since the X chromosome is a sex chromosome and females have two copies while males have only one copy, if the inheritance pattern is recessive, males will be affected, while females need to inherit a mutated gene from both their father and mother in order to be affected. Since men never inherit their X-chromosome from their father, the mutated gene can never pass to a son from his father. Daughters have always inherited one of their X-chromosomes from their father, thus an affected father will always have passed the mutated gene on to his daughters. This daughter will only be a carrier and not affected by the disease, unless she also has inherited the mutated gene from her mother. It is therefore common for X-linked recessive diseases to skip generations of daughters. A female that carry one mutated gene copy have a 50% risk of passing this on to both their sons and daughters.
