What does autosomal dominant mean? There are 23 pairs of chromosomes in humans, 22 of which are autosomes and 1 pair is a sex chromosome. Autosomal dominant inheritance means that the genes that control the disease are located on the autosomes, and if the disease-causing gene is on the autosome, the inheritance of the disease has little to do with gender. Autosomal dominant inheritance means that the defective gene is dominantly expressed and 50% of the children have the possibility of developing the disease. The action of the gene can be influenced by the environment and other genes that alter its phenotypic expression. Therefore, even if the same gene is altered in the same family, very different phenotypes can be expressed, and it only takes one allele of the gene to be abnormal to cause an autosomal dominant disorder. Autosomal dominant disorders, in which there is vertical transmission, are usually considered to have the following rules: one of the parents of the patient has the disease and the average number of children born to the patient and a normal person with and without the disease is equal; when one of the parents has the disease and he or she does not have the disease, his or her offspring will not have the disease; men and women have an equal chance of having the disease; and the incidence of the disease in the children of the patient is 50%.