Answers to Blood Type Questions

Q1: Adam and Julie have blood types B+ and O-

respectively. Their first child is O-. Write the ABO and

Rhesus genotypes of Adam, Julie and their child. What

is the probability of their next child having the same

blood type as Adam?

• Julie is double homozygous recessive, so

this is effectively a testcross and only the

alleles inherited from Adam need to be

considered. For their next child to have

B+ blood type, it would have to inherit IB

and Rh+ from Adam. The probability of

inheriting each is ½, so P(next child B+) =

½ x ½ = ¼ .

Genotypes

Adam

IB/IO; Rh+/Rh-

Julie

IO/IO; Rh-/Rh-

IO/IO; Rh-/Rh-

Answers to Blood Type Questions

Q2: Kwok is a universal recipient (AB+) and his mother is

A+. What are the possible genotypes and phenotypes of

his father?

• Kwok could be IA/IB; Rh+/Rh─ or IA/IB; Rh+/Rh+

• Kwok’s mother must have at least one IA allele and will

be either Rh+/Rh─ or Rh+/Rh+

• Kwok’s IB allele must come from his father, but his father’s

Rhesus genotype could be either Rh+/Rh─ or Rh+/Rh+ or Rh─/Rh─

• So, on the information available Kwok’s father could be :

Genotype Phenotype

IA/IB AB

IB/IB B

IB/IO B

Rh+/Rh─

or

Rh+/Rh+

or

Rh─/Rh─

+ or -