Co-dominance & Multiple Alleles Genetics of Blood
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
Percent of Population that has the O Blood Type by Region in the World
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.
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
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.
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.
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
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.