Question

Study the pedigree chart given below, showing the inheritance pattern of blood group in a family:

Answer the following questions:

[(a)] Give the possible genotypes of individual 1 and 2.
[(b)] Which antigen or antigens will be present on the plasma membranes of the R.B.Cs of individuals ‘5’ and ‘8’?

Hint:

Blood group inheritance follows codominance (A and B alleles) and simple recessiveness (O allele). Genotype must be inferred from both phenotype and offspring data.

Answer 1

•  
  • Individual 1 (B): Possible genotype = $I^B I^O$ 
  • Individual 2 (A): Possible genotype = $I^A I^O$
    (Since their child (individual 8) has blood group O, both parents must carry the $I^O$ allele.)
•  
  • Individual 5 (AB): Antigens present = A and B antigens
  • Individual 8 (O): Antigens present = None (no A or B antigen present on RBC membrane)