Inheritance of a specific disease, condition, or trait depends on the type of chromosome that is affected. It can be either an autosomal chromosome or a sex chromosome. It also depends on whether the trait is dominant or recessive. Sex-linked diseases are inherited through one of the sex chromosomes, which are the X and Y chromosomes.

Dominant inheritance occurs when a variant gene from one parent can cause a disease, even though a matching gene from the other parent is normal. The variant gene dominates the gene pair.

For an X-linked dominant disorder: If the father has the variant X gene, all of his daughters will inherit the disease and none of his sons will have the disease. That is because daughters always inherit their father's X chromosome. If the mother carries the variant X gene, half of all her children (daughters and sons) will inherit the trait.

For example, if there are four children (two boys and two girls) and the mother is affected (she has one variant X and has the disease) but the father does not have the variant X gene, the expected odds are:

• Two children (one girl and one boy) will have the disease
• Two children (one girl and one boy) will not have the disease

If there are four children (two boys and two girls) and the father is affected (he has one variant X gene and has the disease) but the mother is not affected, the expected odds are:

• Two girls will have the disease
• Two boys will not have the disease

These odds do not mean that the children who inherit the variant X gene will show severe symptoms of the disease. The chance of inheritance is new with each conception, so these expected odds may not be what actually occurs in a family. Some X-linked dominant disorders are so severe that males with the genetic disorder may die before birth. Therefore, there may be an increased rate of miscarriages in the family or fewer male children than expected.