Dominance -( IAIO, IBIO)- the phenomenon whereby, in an individual containing two allelic forms of a gene, one is expressed to the exclusion of the other.
Codominance -( IAIB)- a form of dominance wherein the alleles of a gene pair in a heterozygote are fully expressed. This results in offspring with a phenotype that is neither dominant nor recessive.
Multiple alleles- IA, IB & IO - 3-different allelic forms of a gene.