SEX-LINKED DOMINANT
Alternative names:
genetics (sex-linked dominant); inheritance (sex-linked dominant); X-linked dominant
Information:
Definition:
A single abnormal gene on the X chromosome can cause the disease. This disease is transmitted equally to boys and girls. 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 (diseases are not inherited through the Y chromosome).
Dominant inheritance occurs when an abnormal gene from ONE parent is capable of causing disease even though the matching gene from the other parent 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 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 have 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 have the disease.
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 & 1 boy) with disease
- 2 children (1 girl & 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 boys normal
This does not mean that children WILL necessarily be affected; it does mean that EACH child has a chance of inheriting the disorder or of being a carrier.
RELATED TOPICS:
autosomal dominant
autosomal recessive
genetic counseling and prenatal diagnosis
sex-linked recessive
For detailed information, see heredity and disease (genetics).
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