5. The newborn baby of a mother having blood group AB, Rh⁺ and father having blood group O, Rh^–, got mixed withother babies in the hospital. The baby with which of the following blood groups is expected to be of the said couple)
(1) O, Rh⁺      (2) O, Rh^–
(3) AB, Rh^–    (4) B, Rh⁺

Step-by-step Genetic Analysis

Step 1: ABO Possibilities (AB × O)

Mother: AB → genotype I^AI^B [web:122][web:123].

Father: O → genotype ii.

Gametes:

• Mother: I^A or I^B
• Father: i only

Possible child genotypes:

• I^Ai → phenotype A
• I^Bi → phenotype B

Key conclusion: Child can be A or B only. O and AB impossible [web:149].

Step 2: Rh Possibilities (Rh+ × Rh-)

Mother: Rh+ (DD or Dd)

Father: Rh- (dd)

• Rh+ child: Dd (if mother passes D)
• Rh- child: dd (if mother Dd passes d)

Both Rh+ and Rh- possible.

Step 3: Evaluate Each Option

Option 1: O, Rh+

ABO: IMPOSSIBLE (AB×O cannot produce O)

Result: ❌ Not their baby

Option 2: O, Rh-

ABO: IMPOSSIBLE (O impossible)

Result: ❌ Not their baby

Option 3: AB, Rh-

ABO: IMPOSSIBLE (AB impossible – child gets only one A/B allele + i)

Result: ❌ Not their baby

Option 4: B, Rh+ ✅ CORRECT

• ABO: ✅ Possible (I^Bi = Type B)
• Rh: ✅ Possible (Dd = Rh+)

Result: ✅ Genetically compatible [web:125].

Final Conclusion

Only a baby with blood group B, Rh+ could genetically be the child of an AB, Rh+ mother and an O, Rh- father.