Autosomal Dominant Inheritance
In autosomal dominant inheritance, only one copy of a disease allele is necessary for an individual to be susceptible to expressing the phenotype.
With each pregnancy, there is a one in two (50%) chance the offspring will inherit the disease allele.
Unless a new mutation has occurred, all affected individuals will have at least one parent who carries the disease allele.
Autosomal dominant inheritance is often called vertical inheritance because of the transmission from parent to offspring.
Across a population, the proportion of affected males should be equal to the proportion of affected females.
Male-to-male transmission can be observed.
Examples of diseases with autosomal dominant inheritance include myotonic muscular dystrophy and Huntington disease.

3.3 Autosomal Recessive Inheritance
In autosomal recessive inheritance, two copies of a disease allele are required for an individual to be susceptible to expressing the phenotype.
Typically, the parents of an affected individual are not affected but are gene carriers.
With each pregnancy of carrier parents:
There is a one in four (25%) chance the offspring will inherit two copies of the disease allele and will therefore have the phenotype.
There is a one in two (50%) chance the offspring will inherit one copy of the disease allele and will be a carrier.
There is a one in four (25%) chance the offspring will inherit no copies of the disease allele and will not express the phenotype or be a carrier. This individual would not be at risk for passing the disorder on to his/her offspring.