Types of Inheritance

Question 1

Autosomal dominant inheritance?

Answer 1

• Each child has 50% chance of inheriting mutation
• No skipped generations - vertical transmission
• Equally transmitted by men and women
• Only once copy of a gene pair is altered
• Gonadal mosaicism - healthy parents may harbour mutation in SOME cells (e.g. gonads) - recurrences of autosomal dominant conditions in siblings born to unaffected parents.

Question 2

Examples of Autosomal dominance?

Answer 2

1) Adult PKD
2) Huntington disease
3) Marfan syndrome
4) Osteogenesis imperfecta

Question 3

Autosomal recessive inheritance?

Answer 3

• Two germline mutations (one from each parent to develop disease)
• Equally transmitted by men and women
• Usually one generation affected - unless consanguinity
• For 2 carrier parents - risk of each child being affected is 25%
• All offspring of affected individuals will be carriers

Question 4

Examples of autosomal recessive conditions?

Answer 4

1) Cystic Fibrosis
2) Haemochromatosis
3) Spinal Muscular atrophy

Question 5

X-linked inheritance?

Answer 5

• Genes carried on X chromosome
• Men affected more than females since they only have 1 X chromosome.
• All daughters of affected males will be carriers
• No male offspring of affected male can have the disorder since man passes Y chromosome to his son.
• X-linked dominant conditions are rare (Vitamin D resistant Rickets).

Question 6

Examples of X-linked recessive conditions?

Answer 6

1) Duchenne and Becker muscular dystrophy
2) Fragile X syndrome
3) Haemophilia

Question 7

Mitochondrial disorders?

Answer 7

• Exclusively maternally inherited deriving from those present in the cytoplasm of the ovum.
• Mitochondria are inherited exclusively from mother in egg cel
• All offspring of an affected or carrier female are at risk
• All daughters of an affected or carrier female are at his of transmitting condition
• Affected males cannot pass the condition
  E.g. Leber hereditary optic neuropathy, Mitochondrial encephalopathy.