Blood Grouping and Inheritance An example of how we show multiple alleles and codominace

Genotypically speaking blood is quite similar to the other genes we have discussed. It uses a capital letter to represent a dominant trait It also uses a lower case letter to represent a recessive trait I i

I i From a dominant and recessive allele we can assume that we have 3 possible combinations II – Homozygous dominant Ii – Heterozygous ii – Homozygous recessive But with blood there is more than just two possible alleles to consider

When we talk about the ABO blood groups there are actually 3 alleles that are responsible for the different groups The “O” trait has the first trait and is the lone recessive allele and is written as “ i ” The other two traits, “A” and “B” are both dominant so they both use the capital letter “ I”

PROBLEM - But with “ I” written as is there is no way to decipher if it is an A allele or a B allele SOLUTION – For each separate trait the allele will have an accompanying superscript letter. IAIA IBIB This is not done to confuse you The capital “ I” tells you the trait is a dominant allele and the superscript just helps you figure out which dominant allele it is.

So instead of just three possible genotypes, II – Homozygous dominant Ii – Heterozygous ii – Homozygous recessive We actually have 6 possible genotypes IAIAIAIA IBIBIBIB IAiIAi ii IBiIBi IAIBIAIB And four possible Phenotypes

Hopefully that helps you out