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Genetics
Genetics

Sex-linked dominant
Alternative Names:
Inheritance - sex-linked dominant; Genetics - sex-linked dominant; X-linked dominant

Information:
A single abnormal gene on the X chromosome can cause the disease. This disease is likely to be transmitted to boys and girls, however boys may not survive. This is a rare mode of transmission.

BACKGROUND:
The inheritance of genetic diseases, abnormalities, or traits is described by both the type of chromosome the abnormal gene resides on (autosomal or sex chromosome), and by whether the gene itself is dominant or recessive.

Autosomally inherited diseases are inherited through the non-sex chromosomes, pairs 1 through 22. Sex-linked diseases are inherited through one of the "sex chromosomes" (the X chromosome or the Y chromosome).

Dominant inheritance occurs when an abnormal gene from ONE parent is capable of causing disease even though there may be a matching gene from the other parent that is normal. The abnormal gene dominates the outcome of the gene pair.

Recessive inheritance occurs when BOTH matching genes must be abnormal to produce disease. If only one gene in the pair is abnormal, the disease is not manifest or is only mildly manifest. However, the genetic predisposition to disease can be passed on to the children.

STATISTICAL CHANCES OF INHERITING A TRAIT:
For an X-linked dominant disorder: If the father carries the abnormal X gene, all of his daughters will inherit the disease and none of the sons will have the disease. If the mother carries the abnormal X gene half of all their children (daughters and sons) will inherit the disease tendency.

In other words, if it is assumed that 4 children are produced (2 male and 2 female), the mother is a carrier (1 abnormal X, she has disease), and the father is normal, the STATISTICAL expectation is for:
  • 2 children (1 girl and 1 boy) with disease
  • 2 children (1 girl and 1 boy) normal
If it is assumed that 4 children are produced (2 male and 2 female), the father is a carrier (abnormal X, he has disease), and the mother is normal, the STATISTICAL expectation is for:
  • 2 girls with disease
  • 2 normal boys
This does not mean that children WILL necessarily be affected.
RELATED TOPICS:
Autosomal dominant
Autosomal recessive
Genetic counseling and prenatal diagnosis
Sex-linked recessive

For detailed information, see heredity and disease (genetics).
Review Date: 8/12/2001
Reviewed By: David G. Brooks, M.D., Ph.D., Division of Medical Genetics, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.
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