1. Co-dominance & Multiple Alleles Genetics of Blood

2. Human Blood Type One gene for blood type
Three different alleles (IA, IB, i)
IA and IB are co-dominant and i is recessive
6 possible genotypes
4 possible phenotypes
Genotype
Phenotype
IAIA or IAi
Type A
IBIB or IBi
Type B
IAIB
Type AB ii
Type O

5. Co-dominance
·  Occurs when two different alleles for the same characteristic are fully expressed in the phenotype (e.g. Blood Type AB)
· another example of co-dominance is in horses and shorthorn cattle where two alleles are expressed at the same time.
· If one parent is homozygous red and the other is homozygous white, the offspring will be a pinkish colour termed “roan”, a blend of red and white. However, each individual hair in the coat is either completely white or completely red.

6. Practice Questions
1. Suppose a man with type AB blood and a woman with type O blood have a child. What are the possible blood types of the child? IA IB i
IAi
IBi
50% Type A
50% Type B

7. 2. Two parents have type AB blood
2. Two parents have type AB blood. What is the chance that they will have a child with type O blood? IA IB
IA IA
IAIB
IA IB
IBIB
There is a 0% chance that they will have a child with type O blood.

8. 3. Suppose a man has type B blood and a woman has type A blood
3. Suppose a man has type B blood and a woman has type A blood. Could they have a child with type O blood? IB i IA
IAIB
IAi
IBi ii
Yes, if both parents are heterozygous, it is possible for them to have a child with type O blood.

9. Blood Type Compatibility
Can Give Blood To
Can Receive Blood From A
A, AB
A, O B
B, AB
B, O O
A, B, AB, O AB
Type O is the universal donor
Type AB is the universal recipient

11. 4. Suppose that emergency surgery must be performed on a Type B patient during a blood shortage. The patient’s mother is type O, but cannot reach the hospital in time. Would blood from the patient’s father be suitable?
Possible father type 1
Possible father type 2 IA IB i
IAi
IBi
IA i IB i
IBi ii
IB i
The patient’s father could be type AB or type B. If the father is type B, he is a suitable donor. If the father is type AB, he is not a suitable donor.