What if the heterozygous trait exhibited codominance? in this case, two alleles can code for co-dominant traits. That is, neither is dominant over the other. Blood type is an example of this:
A is codominant to BA is dominant over O
B is dominant over O
Possible genotypes:
heterozygous AB blood gives both type A protein and type B protein on the erythrocytes.
homozygous AA gives blood type A protein on the erythrocytes
homozygous BB is blood type B protein on the erythrocytes
Heterozygous AO is gives blood type A
Heterozygous BO is blood type B
homozygous recessive OO gives blood type O .
There is neither A or B on erythrocytes.
You have heard that blood type is important for blood transfusions. That is because the immune system will always attack an unknown protein. Thus
type A person can receive type A blood, and will reject type B blood
type B person can receive type B blood and will reject type A blood.
type AB person can receive type A blood and Type B blood
Type O person can receive nobody's blood except from another type O
Everyone can receive type O, No-one can receive type AB
Blood type is heritable and that means you can sometimes deduce genotype by looking at phenotype. Here is a sample question:
