A functional alteration in one of the gene couple located on the same locus is enough for the emergence of the diseases is an example for autosomal dominant inheritance. These types of diseases generally are related to structural proteins. Genetic disease appears in every generation and affected individual has definitely obtained this disorder from at least one of his/her parents. Probability of the disease to be seen in children of an affected parent is 50%, regardless the gender of the kids.
Unlike classical model of genetics mentioned above, most of the autosomal dominant diseases arise by de novo mutations, therefore affected parents may not be identified. Furthermore, the degree of severity and level of expression (expressivity) vary from person to person of affected individual in phenotype in autosomal dominant diseases or the effect of mutant gene may not be seen in afflicted person (penetrance). That is why disease may not be seen in all generations and family pedigree does not show a vertical pattern.
Another exception concerning this type of disease is that disease arises from mutations occurred in the gametes of even one parent. Transmittance for such de novo mutations is thought not be to be recurrent and the risk of inheritance changes depending on the ratio that how much of these mutations will be passed on via germ cells to the next generations. Such exceptional cases should be taken into consideration for autosomal dominant diseases when the diseases are in the concern of genetic consultants. Finally, all family members should be examined carefully.