Genetics

Question 1

What is the risk of inheriting an autosomal dominant condition?

Answer 1

50% if parent affected

Question 2

True or false: Male and female offspring can be affected by autosomal dominant conditions.

Answer 2

True

Question 3

What is the risk of inheriting an autosomal recessive condition?

Answer 3

1 in 4 risk of condition. Both parents carriers.

2 in 3 risk of unaffected children being carriers.

Question 4

Which genetic mode of inheritance is most associated with consanguinity?

Answer 4

Autosomal recessive

Question 5

Which mode of inheritance affects male offspring more commonly than females?

Answer 5

X-linked

Females have two X chromosomes, meaning a normal gene usually compensates for the faulty gene they carry. Males, however, only have one X chromosome and therefore a faulty gene will be expressed as it is unopposed.

Question 6

True or false: Sons always inherit x-linked conditions from their fathers.

Answer 6

False. Fathers pass on a Y chromosome to their sons, therefore affected males must inherit the gene from their mothers.

Question 7

True or false: 100% of daughters from affected men are carriers of an x-linked condition.

Answer 7

True.

Men only have one X chromosome and will always pass this on to their daughters. Therefore, a male with an x-linked condition will always pass their affected gene to any daughters they may have. Daughters are usually unaffected, however, as they will have a ‘normal’ x chromosome from their mother to compensate.

Question 8

What is the risk of inheriting an x-linked condition?

Answer 8

50% of sons with carrier mother will be affected

0% of sons of affected father will be affected

50% of daughters of carrier mothers are carriers

100% of daughters of affected fathers are carriers

If a mother carries an x-linked condition, her sons have 1 in 2 chance of being affected by the disease and her daughters each have a 1 in 2 chance of being a carrier of the disease (each may inherit the normal or the abnormal chromosome).

Question 9

Mode of inheritance: Haemophilia A

Answer 9

X-linked

Question 10

Mode of inheritance: Thalassaemia

Answer 10

Autosomal recessive

Question 11

Mode of inheritance: Cystic fibrosis

Answer 11

Autosomal recessive

Question 12

Mode of inheritance: Duchenne muscular dystrophy

Answer 12

X-linked

Question 13

Mode of inheritance: Achondroplasia

Answer 13

Autosomal dominant

Question 14

Mode of inheritance: Sickle cell

Answer 14

Autosomal recessive

Question 15

Mode of inheritance: von Willebrand disease

Answer 15

Autosomal dominant

Question 16

Mode of inheritance: Marfan syndrome

Answer 16

Autosomal dominant

Question 17

Mode of inheritance: Huntingdon’s

Answer 17

Autosomal dominant (trinucleotide repeat)

Question 18

Mode of inheritance: Myotonic dystrophy

Answer 18

Autosomal dominant

Question 19

Mode of inheritance: G6PD deficiency

Answer 19

X-linked

Question 20

Mode of inheritance: Haemophilia B

Answer 20

X-linked