Question

Two individuals have a baby. The father has blood type O and is a heterozygote for the Bombay phenotype at the H locus. The mother has blood type AB and is a heterozygote for the Bombay phenotype. What is the probability their offspring can accept blood from a type A donor?

1/8

1/4

3/8

1/2

3/4

Answer 1

ABO locus determines whether the antigens on the RBC are produced or not, and H locus determines whether these antigens are presented on the RBC,

IA- A antigen

IB- B antigen

i- no antigens are produced from i allele.

H- links the antigen to the RBC

h-can not link antigen to RBC

when the genotype at the H locus is hh then the phenotype is O type blood regardless of the genotype at the ABO locus, so this is an example of recessive epistasis.

the father has blood type O and is a heterozygote for the Bombay phenotype at the H locus so his genotype is iiHh and the mother has blood type AB and is a heterozygote for the Bombay phenotype so her genotype is IAIBHh.

IAIBHh * iiHh

	IAH	IAh	IBH	IBh
iH	IAiHH ( A type blood)	IAiHh ( A type blood)	IBiHH ( B type blood)	IBiHh ( B type blood)
ih	IAiHh( A type blood)	IAihh( O type blood)	IBiHh ( B type blood)	IBihh( O type blood)

to receive blood from a donor who has A type blood, both H and A antigens has to be present on the RBC of the recipient, that is both IA and H allele has to be present, so the blood group of the recipient has to be O type.

probability their offspring can accept blood from a type A donor= number of progeny with A type blood/total number=3/8

so the answer is 3/8