In which of the following patterns of inheritance are both males and females affected but there is no paternal transmission of the condition?
Exam Question Oct 2014
Fathers cannot pass on mitochondrial disorders as they do not contribute mitochondria to their children (there are no mitochondria in sperm).
Autosomal recessive19%Mitochondrial20%Autosomal dominant20%X-linked recessive20%X-linked dominant21%
Exam Question Oct 2014
Fathers cannot pass on mitochondrial disorders as they do not contribute mitochondria to their children (there are no mitochondria in sperm).
Inheritance (patterns)
Autosomal dominant conditions:-
- All forms of transmission observed (male to male, male to female, female to female)
- Transmitted from one generation to the next (vertical transmission)
- Males and female affected in equal proportions
- Parents usually one affected heterozygote and one unaffected homozygote
- If only one parent affected there is a 50% chance that a child will inherit the mutated gene
Autosomal recessive conditions:-
- Males and female affected in equal proportions
- Two copies of the gene must be mutated for a person to be affected
- both parents' usually unaffected heterozygotes
- Two unaffected people who each carry one copy of the mutated gene have a 25% chance with each pregnancy of having a child affected by the disorder
X-linked dominant conditions:-
- Males and females are both affected in these disorders, with males typically being more severely affected than females
- The sons of a man with an X-linked dominant disorder will all be unaffected
- A woman with an X-linked dominant disorder has a 50% chance of having an affected foetus
X-linked recessive conditions:-
- Males are more frequently affected than females
- Transmitted through carrier females to their sons (knights move pattern)
- Affected males cannot pass the condition onto their sons
- A woman who is a carrier of an X-linked recessive disorder has a 50% chance of having sons who are affected and a 50% chance of having daughters who are carriers
Y-linked conditions:-
- Every son of an affected father will be affected
- Female offspring of affected fathers are never affected
Mitochondrial inheritance:-
- Mitochondria are inherited only in the maternal ova and not in sperm
- Males and females affected, but always being maternally inherited
- An affected male does not pass on his mitochondria to his children, so all his children will be unaffected
