Sex-linked dominant is a rare way that a trait or disorder can be passed down through families. A single abnormal gene on the X chromosome can cause a sex-linked dominant disease.

Related terms and topics:

• Gene
• Chromosome
• Inheritance
• Heredity and disease
• Genetic counseling and prenatal diagnosis
• Sex-linked recessive
• Autosomal dominant
• Autosomal recessive

Inheritance of a specific disease, condition, or trait depends on the type of chromosome affected (autosomal or sex chromosome) whether the trait is dominant or recessive. Sex-linked diseases are inherited through one of the sex chromosomes (the X or 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.

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) and the mother is affected (1 abnormal X, she has disease) but the father is not, the STATISTICAL expectation is for:

• 2 children (1 girl and 1 boy) with disease
• 2 children (1 girl and 1 boy) without the disease

If it is assumed that 4 children are produced (2 male and 2 female) and the father is affected (abnormal X, he has disease) but the mother is not, the STATISTICAL expectation is for:

• 2 girls with disease
• 2 boys without the disease

This does not mean that children WILL necessarily be affected.