Autosomal Dominant Genes

Autosomal Dominant (AD) Genes

• Autosomal Dominant (AD) single gene traits have controlling gene alleles located on an autosomal chromosome.
• The trait is expressed regardless of whether the person is homozygous or heterozygous for the dominant allele.
• The trait appears in both sexes with equal frequency.

Characteristics of Autosomal Dominant Patterns of Inheritance

• The trait is found in approximate equal distribution between male and female family members.
• The trait has no carrier status (the person with even one dominant allele expresses the trait).
• The trait appears in every generation with clear transmission from parent to child.
• The risk for an affected person who is heterozygous for the dominant allele to pass the trait to their child is 50% with each pregnancy.
• The risk for an affected person who is homozygous for the dominant allele to pass the trait to their child is 100% with each pregnancy.
• Unaffected people do not have the allele and have essentially zero risk for transmitting the trait to their children.

Examples of Autosomal Dominant Disorders

• Familial adenomatous polyposis coli (GIT)
• Hereditary Nonpolyposis Colon Cancer (HNCC)
• Hereditary spherocytosis (Haematology)
• Van Willebrand disease (Haematology)
• Neurofibromatosis (types 1 and 2)
• Huntington disease
• Adult polycystic kidney disease (types 1 and 2)

Autosomal Dominant Single Gene Traits

• Blood type A
• Blood type B
• Free earlobes (not attached to the head)
• Taste sensitivity to phenylthiocarbamide (PTC)
• Widow's peak