Answer to Question #176773 in Genetics for John

Question

Explain the concept of ‘multiple alleles’. Use the ABO blood grouping system to illustrate your answer. Produce a table to illustrate all possible phenotypes and their respective genotypes

Answer 1

Three or more alternative forms of a gene (alleles) that can occupy the same locus are called multiple alleles. Multiple alleles cannot be observed in the genotype of a diploid individual but can be observed in a population.The number of genotypes that can occur for multiples alleles is given by expression where n=number of alleles.ABO blood groups are the best examples for multiple allelism in human beings. The ABO blood group system was proposed by Karl Landsteiner. The blood group A, B, AB and O types are characterised by the presence or absence of antigens on the surface of RBC.

• Blood type A person have antigen A on their RBCs and anti B antibodies in the plasma.
• Blood type B person have antigen B on their RBCs and anti A antibodies in the plasma.
• Blood type AB person have antigen A and B on the RBCs and no antibodies in the plasma.
• Blood type O person have no antigens on their RBCs and both anti-A and anti-B antibodies are present in the plasma.

Bernstein discovered that these phenotypes were inherited by the interactions of three autosomal alleles of the genes named ‘I’ located on chromosome 9.I^A, I^B and I^O are the three alleles of the gene.The alleles I^A and I^B are responsible for the production of the respective antigen A and B.The alleles IO does not produce any antigen.The alleles I^A and I^B are dominant to the allele I^o, but co-dominant to each otherA child receives one of the three alleles from each parent, giving rise to six possible genotypes and four possible blood types.The genotypes are , I^AI^A, I^AI^O, I^BI^B, I^BI^O, I^AI^B, I^OI^O.The phenotypic expressions of I^AI^A, I^AI^O are A – type of bloodThe phenotypic expressions of I^BI^B, I^BI^O, are B- type of bloodThe phenotypic expression of I^AI^B is AB blood typeThe phenotypic expression of I^OI^O is O-type of blood.