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The following diagram represents a two generation pedigree showing the blood
groups of the individuals. The female has been married to two different
individuals.
O
A
AB
Key
1st generation
1
2
Male
3
Female
B
O
A
AB
2nd generation
1
(a)
2
3
4
Define the term co-dominant alleles. See topic 4.3.1
Be aware that blood types are also an example of multiple alleles- see
topic 4.3.3. Remember to use the symbols used by the IBO
Ia for allele type A, dominant to i
Ib for allele type B, dominant to i
I for the type O allele- recessive to the other 2 alleles
(1)
(b)
Deduce with a reason the probable father of 2nd generation-1.
2nd generation-1 refers to the first square on the leftin the bottom row. First step is to write
the full genotypes for the 2nd G -1; since his mother (1st G 2) is type A and has an type O
offspring, 2nd G-1 must be hetereozygous Ibi . This then in turn means that the father must
have given the Ib allele and this would mean the true father must be the type_____ male.
(2)
(c)
If 2nd generation-3 marries a man with blood group AB, predict the
possible genotypes of the children.
Since you know that the new husband has the genotype IaIb and the wife has Ia?, you have
2 choices.
1. if the wife is heterozygous, Ia i, then draw a punnett grid for genotypes A, B and AB.
2. if the wife is homozygous, Ia Ia, then draws the 2nd punnett grid for genotypes A and AB
There are 6 marks for this, since there are two possibilities
(Total 6marks)
(3)