Inheritance (patterns)

Question 1

Autosomal dominant conditions:-

Answer 1

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

Question 2

Autosomal recessive conditions:-

Answer 2

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

Question 3

X-linked dominant conditions:-

Answer 3

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

Question 4

X-linked recessive conditions:-

Answer 4

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

Question 5

Y-linked conditions

Answer 5

Every son of an affected father will be affected

Female offspring of affected fathers are never affected

Question 6

Mitochondrial inheritance

Answer 6

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