Inheritance Patterns

Autosomal Dominant Inheritance

• Individuals affected in every generation
• Some carriers may not manifest disease
• Males and females have equal chance of passing on mutation
• 50% risk to children

Autosomal Recessive Inheritance

• May be only one generation affected
• Carriers typically do not have condition
• Both parents must be carriers of the mutation
• 25% risk to children

X-linked Inheritance

• No male-to-male transmission
• Though rare, females can be affected if they inherited two mutations
• Many female carriers (one mutation) will have no symptoms; those that do have milder symptoms than seen in males
• Risk for inheriting an X-linked condition:
  • 100% for daughters of affected fathers to be carriers
  • 0% for sons of affected fathers to be affected
  • 50% for daughters of carrier or affected mothers to be carriers
  • 100% for sons of affected mothers to be affected
  • 50% for sons of carrier mothers to be affected

Complex Inheritance

• No clear Mendelian pattern of inheritance
• Clustering of biologically related conditions in the family
• Risk estimates based primarily on empiric data
• The chance of developing a complex trait depends on several factors, which may include:
  • The number of relatives affected with a condition (or related conditions)
  • How closely one is related to the affected individual(s)
  • Similarity of the shared environment and lifestyle factors
  • Severity of the condition in the affected relative
  • The age at onset in the affected family member
  • The sex of the affected family member
  • Ethnicity

  Reviewed November 2021