(a)Explain the phenomena of multiple allelism and codominance taking the ABO blood group as an example.
(b)What is the phenotype of the following: (i) A, (ii) ii

Hint: In particular, multiple allelism is the situation wherein three or more alleles of a gene are available. Codominance is a sort of inheritance in which the alleles of a gene pair during a heterozygote are completely expressed.

Complete answer:
(a) Multiple allelism means three or more sorts of a gene that will occupy an equivalent locus but only two out of three are often present in an individual at an equivalent time. For instance, the ABO blood type system is controlled by three genes but only at a time is
present within the individual.
Codominance is a sort of dominance during which both the alleles express themselves equally during a heterozygous condition. This leads to offspring which are neither dominant nor recessive. For example, in an individual with AB blood type, both the A and B alleles exhibit themselves equally.
(b) (i) Phenotypes of Ai are going to be blood type A since allele A is dominant over allele i.
(ii) Phenotypes of ii are going to be an O blood group since the allele is recessive and expresses itself within the homozygous condition.

Additional Information: Individuals with blood type ABO exhibit Codominance. A and B are dominant in reference to O, however, they're not dominant against one another.
Features of multiple alleles
-The same genes have quite two alleles.
- All multiple alleles in homologous chromosomes occur on the particular loci.
- A chromosome or gamete only has one group allele.
- Each human contains only two separate gene alleles, one for every homologous pair of chromosomes carrying the gene.
- Multiple alleles express various alternatives of 1 trait

Note: Codominance essentially means no allele can block or mask the expression of the opposite allele. Different alleles can express codominance, dominance-recessive manners, or incomplete dominance. The ABO blood types were discovered by Landsteiner in 1901; he received the Nobel Prize in Physiology or Medicine in 1930 for this discovery. ABO blood types also are present in other primates like apes and Old World monkeys.