What is X-linked recessive inheritance?

Genetic diseases with an X-linked recessive inheritance pattern usually affect only the males in a family. These diseases are inherited via mutations on the X chromosome. Females have two X chromosomes and therefore, if they inherit only one X chromosome with the mutated gene and one with the functional gene, they can exhibit a healthy “normal” phenotype. The functional gene is “masking” the effect of the mutated gene. Females with the mutated gene on one of their X-chromosomes are referred to as “carriers”. On the other hand, males have one X chromosome and one Y chromosome. If a male inherits a mutated gene on the X chromosome, there is no alternative functional gene to compensate or “mask” the effects of the mutation. This means the male will exhibit the disease phenotype. A common example of an X-linked recessive disorder is red-green colour blindness; to have this trait, males must inherit the mutated gene on their X-chromosome from their mother, however females must inherit the mutated gene on both their X-chromosomes to have the disease. This can explain why significantly more males (between 7 to 10%) are affected with the trait, compared to females (between 0.49 to 1%). Other examples of X-linked disorders include, haemophilia A and Duchenne muscular dystrophy.