Autosomal dominant

From Freepedia

An autosomal dominant gene is an abnormal gene on one of the autosomal (non-sex determining) chromosomes. Because it is dominant, it need only exist in the inherited chromosomes of one parent for it to cause disease. The chances of an autosomal dominant disorder being inherited are 50% if one parent has the gene. Some diseases inherit in this fashion but still affect less than 50% of the offspring; in this case the disease is termed of having incomplete penetrance.

For example, pretend that there are two people. One has an abnormal gene and the other one has a normal gene. The offspring of the two would have the abnormal gene (and the disease). This is because the abnormal gene is dominant.

The dominant genes are not always abnormal genes. Important genes like the tumor supressor genes BRCA1/2 are passed to the offsprings as dominant. In this way it is sure that these genes are expressed. In case of mutations these genes can cause serious diseases (in this case familiar breast cancer).

Other forms of inheritance are: autosomal recessive, X-linked and mitochondrial.