Q.3 If the blood groups of mother and father are AB and O, respectively, what are the blood groups
possible for their child?
(A) AB or A (B) AB (C) A or B (D) AB, A, B or O

Mother with blood group AB (genotype I^A I^B) and father with O (genotype ii) can only produce children with blood groups A or B. This follows ABO inheritance rules where the father contributes only i alleles, pairing with either I^A or I^B from the mother to yield I^A i (A) or I^B i (B).

Parental Genotypes

AB blood group requires codominant I^A and I^B alleles, so mother’s genotype is I^A I^B. O blood group is recessive homozygous ii, meaning father contributes only i alleles.

Punnett Square Analysis

Cross I^A I^B × ii yields:

Offspring genotypes: 50% I^A i (A), 50% I^B i (B). No ii (O) or I^A I^B (AB) possible.

Option Evaluation

• (A) AB or A: Incorrect, excludes B; AB impossible as father lacks neither allele.

• (B) AB: Incorrect, child cannot inherit both I^A and I^B without father’s contribution.

• (C) A or B: Correct, matches Punnett square outcomes exclusively.

• (D) AB, A, B or O: Incorrect, includes impossible AB and O (requires ii from both parents).

Correct answer: (C) A or B.

Blood groups AB mother O father child possible outcomes follow classic Mendelian codominance in ABO system, crucial for CSIR NET Life Sciences genetics prep. When mother has AB blood (I^A I^B) and father O (ii), child inherits i from father and either I^A or I^B from mother, yielding A or B only—no AB or O.

Genetics Basics

ABO loci have I^A, I^B (codominant), i (recessive). AB parent passes one dominant allele; O passes i, masking neither for AB nor enabling O phenotype.

Punnett Square Breakdown

Visual cross confirms 50% A (I^A i), 50% B (I^B i):

Real-world exceptions rare (e.g., mutations), irrelevant for exam.

Exam Relevance

CSIR NET questions test such crosses; option (C) A or B fits perfectly, eliminating others via allele impossibility.