Multiple allele so far we have studied traits or genes that are coded for by just two alleles. like in rabbits, there was one allele for brown hair color and one allele for white hair. however, some traits are coded for by more than two alleles. one of these is blood type in humans. this is a violation of mendel’s principle of unit characteristics. 5. in humans, there are four types of blood; type a, type b, type ab, and type o. the alleles a and b are codominant to each other and the o allele is recessive to both a and b alleles. so a person with the genotype aa or ao will have a type of blood. (5pts) a. what possible genotypes will produce b type of blood