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What is an X-linked recessive condition?

If a condition is X-linked recessive, a female will not show any symptoms or features of the condition because she has a second copy of the gene on her other X chromosome. (Females have two X chromosomes (sex chromosomes which are structures in our cells that contain genetic information) and males have one X and one Y.) She will be a carrier of the condition. Carriers typically do not show any signs of the condition but are at risk of passing the mutation on to offspring.

This means that sons of a woman carrying a mutation for an X-linked recessive condition have a 50% chance of being affected and daughters have a 50% chance of being a carrier of the condition. Males who inherit a mutation will be affected with the condition because they only have one copy of the X chromosome. Affected males will have unaffected male offspring because they pass on their Y chromosome to sons. All the daughters of affected males will be carriers because the only copy of an X that the affected male has to pass on to female offspring carries a mutation.

Duchenne muscular dystrophy, hemophilia and color-blindness are examples of an X-linked recessive condition. X-linked recessive conditions are carried on the X chromosome and are expressed phenotypically when there is no second X chromosome with a nonaffected allele. Thus, they are transmitted from carrier mothers to affected sons. In these conditions, each female carrier has a 50% chance of transmitting the condition to a male offspring and essentially a 0% chance of transmitting the condition to a female offspring. Each female offspring, however, has a 50% chance of being a carrier like her mother.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.