Early concepts of dominance and recessiveness were first used in conjunction with autosomal traits, and then applied to 'sex'-linked traits to distinguish X-linked recessive and X-linked dominant inheritance. Our modern concepts of Mendelian (including X-linked) inheritance originated just after the turn of the last century. Duplication for commercial use must be authorized in writing by ADAM Health Solutions.The existence of X-linked disorders in humans has been recognized for many centuries, based on lessons in religious texts and observations of specific human families (e.g., color blindness or Daltonism). Links to other sites are provided for information only - they do not constitute endorsements of those other sites. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

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is among the first to achieve this important distinction for online health information and services. follows rigorous standards of quality and accountability. is accredited by URAC, for Health Content Provider (URAC's accreditation program is an independent audit to verify that A.D.A.M. This is called 'skewed X-inactivation.' These females may have symptoms similar to those of males, or they may have only mild symptoms.Ī.D.A.M., Inc. However, this is not technically correct.įemale carriers can have a normal X chromosome that is abnormally inactivated.

The odds of either of these two scenarios are so low that X-linked recessive diseases are sometimes referred to as male only diseases.

100% chance of the child having the disease, whether boy or girl.

If both the mother and the father have the disease, the expected outcomes are: In each pregnancy, if the mother is a carrier and the father has the disease, the expected outcomes are: This could occur in the two scenarios below. An abnormal gene on the X chromosome from each parent would be required, since a female has two X chromosomes. This means that none of his children would actually show the signs of the disease, but the trait could be passed to his grandsons.įemales can get an X-linked recessive disorder, but this is very rare.

50% chance of a having a girl without the disease who is a carrier.

If the father has the disease and the mother is not a carrier, the expected outcomes are:

25% chance of a carrier girl without disease.

In each pregnancy, if the mother is a carrier of a certain disease (she has only one abnormal X chromosome) and the father is not a carrier for the disease, the expected outcome is: Diseases such as hemophilia and Duchenne muscular dystrophy occur from a recessive gene on the X chromosome. Because of that, it doesn't protect the male. However, the Y chromosome doesn't contain most of the genes of the X chromosome. The Y chromosome is the other half of the XY gene pair in the male. A single recessive gene on that X chromosome will cause the disease. X-linked recessive diseases most often occur in males.

Sex linked dominant traits