4. In a hospital three babies were mixed up. The blood group of the babies were A. B and AB. In order to identify the parents of the babies, the blood groups of the parents were determined. The results obtained were:Parent set 1 —A and AB
   Parent set 2 — AB and O
   Parent set 3— B and AB

   Which of the following conclusions can be definitively made?

(1)The baby With blood group A is the child of the parent set 2.
(2) The baby with blood group AB is the child of the parent set 1.
(3) The baby with blood group B is the child of the parent set 3.
(4) The parentage of none of the babies can be determined from the given information.

Step-by-step solution

Step 1: Possible child types from each parent set

ABO genetics: A = I^AI^A, B = I^BI^B, O = ii [web:119][web:123].

Parent set 1: A × AB

• A parent: I^AI^A or I^Ai
• AB parent: I^AI^B
• Possible children: A, B, or AB

Parent set 2: AB × O

• AB: I^AI^B
• O: ii
• Possible children: A or B only (no AB)

Parent set 3: B × AB

• B parent: I^BI^B or I^Bi
• AB parent: I^AI^B
• Possible children: A, B, or AB

Step 2: Check each option

Babies available: A, B, AB

• “Baby A is child of set 2”: Set 2 can produce A, but so can sets 1 & 3
• “Baby AB is child of set 1”: Set 1 can produce AB, but so can set 3
• “Baby B is child of set 3”: Set 3 can produce B, but so can sets 1 & 2

No unique assignment possible – every baby type compatible with ≥2 parent sets [web:126].

Conclusion

Option (4): The parentage of none of the babies can be determined from the given information.