What are multiple alleles ? Describe multiple alleles with the help of ABO blood group in man.
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.
IA, IB and IO are the three alleles of the gene.
The alleles IA and IB are responsible for the production of the respective antigen A and B.
The alleles IO does not produce any antigen.
The alleles IA and IB are dominant to the allele Io, but co-dominant to each other
A child receives one of the three alleles from each parent, giving rise to six possible genotypes and four possible blood types.
The genotypes are , IAIA, IAIO, IBIB, IBIO, IAIB, IOIO.
The phenotypic expressions of IAIA, IAIO are A – type of blood
The phenotypic expressions of IBIB, IBIO, are B- type of blood
The phenotypic expression of IAIB is AB blood type
The phenotypic expression of IOIO is O-type of blood.
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.
IA, IB and IO are the three alleles of the gene.
The alleles IA and IB are responsible for the production of the respective antigen A and B.
The alleles IO does not produce any antigen.
The alleles IA and IB are dominant to the allele Io, but co-dominant to each other
A child receives one of the three alleles from each parent, giving rise to six possible genotypes and four possible blood types.
The genotypes are , IAIA, IAIO, IBIB, IBIO, IAIB, IOIO.
The phenotypic expressions of IAIA, IAIO are A – type of blood
The phenotypic expressions of IBIB, IBIO, are B- type of blood
The phenotypic expression of IAIB is AB blood type
The phenotypic expression of IOIO is O-type of blood.
