Figure 1: The three most common hereditary transmissions. Autosomal dominant transmission indicates that the patient displaying the characteristic feature is heterozygote for the responsible mutation. Full penetrance of the mutation leads to a reliable diagnosis of the genotype through analysing the phaenotype.
In an autosomal recessive inheritance transmission, the patient showing the characteristic feature must have two causative mutations, either homozygote or compound heterozygote. The parents of the patient are phaenotypically inconspicuous, although they are heterozygote. If the mutation responsible for the disease is located on the x-chromosome, this results in a predominance for male patients. Mothers of the patient are phaenotypically inconspicuous (see text for variance). They are heterozygote and thus carriers for the disease.