A person with unknown blood group under ABO system, has suffered much blood loss in an accident and needs immediate blood transfusion. His friend who has vaild certificate of his own blood type, offers for blood donation without delay. What would have been the type of blood group of the donor friend ?

Explanation

Bernstein- proposed the genetic basis of ABO blood grouping. The genetic basis of ABO blood grouping is mainly dependent on the three alleles `I^A, I^B and I^O` on the gene I, located in chromosome 9. The alleles `I^A and I^B` are responsible for the production of the respective antigens A and B on the surface of RBC. The allele `I^@` does not produce any antigen on the surface of RBC. The alleles `I^A and I^B` are dominant to the allele, `I^O` but co-dominant to each other `(I^A=I^B gt I^O)`
A child receives one of the three alleles from each parent, giving risk to six possible genotypes and four possible blood types. The genotypes are `I^A I^A, I^A I^O, I^B I^B ,I^B I^O, I^A I^B I^O I^O`
The phenotypic expression of `I^A I^A and I^A I^O` are A type blood
THe phenotypic expression of `I^B I^B and I^B I^O` are B type blood, and that of `I^A I^B` is AB blood type. The phenotype `I^O I^O` is O -type blood.