Genetic risk calculation

Question 1

Autosomal recessive inheritance

Answer 1

25% risk in offspring
M and F affected equally
Usually no previous family history needed
Commonly affects siblings

Question 2

Example of autosomal recessive disease

Answer 2

Sickle cell and CF

Question 3

What is CF?

Answer 3

Mutation of CFTR = thick mucus in pancreas and lungs

Question 4

What is sickle cell disease?

Answer 4

Abnormal Hb causing sickling of RBCs

Haemolytic anaemia, abnormal cells block small vessels = short life span

Question 5

What is genotype?

Answer 5

At DNA level

Question 6

What is phenotype?

Answer 6

Physical appearance

Question 7

Punnet squares

Answer 7

Predicts genotype of offspring
Normal allele = A
Mutant allele = a

Question 8

How to calculate risk to child

Answer 8

Mother carrier risk x father carrier risk x 1/4

Question 9

How do you calculate carrier risk as you move away from a known carrier?

Answer 9

Probability of being a carrier
halves for each degree of
relationship away from the
known carrier in a family

Question 10

Hardy-Weinburg equations

Answer 10

p+q = 1

p2 + 2pq + q2 = 1

Question 11

What do the different letters represent in Hardy Weinburg?

Answer 11

P = normal allele, q = mutant 
p2 = homozygous normal frequency 
q2 = homozygous mutant frequency 
2pq = heterozygous frequency