Q93. A man, whose mother and father had blood groups A and O respectively,
marries a woman with blood group AB. If the man has blood group A, then
the number of different blood groups possible among their children will be
_________ (in integer).

Blood Group Genetics Basics

The ABO blood group system follows codominance for A and B alleles (I^A, I^B), with O (i) recessive. A person with blood group A has genotype I^A I^A or I^A i. Blood group O is ii, AB is I^A I^B.

Man’s Parental Genotype Analysis

Father (O) has genotype ii, so contributes i. Mother (A) must be I^A i, because if I^A I^A, the man (A) could not receive i from her to express A (which requires at least one I^A). Thus, man inherits I^A from mother and i from father, making his genotype I^A i.

Woman’s Genotype

The woman has blood group AB, so her genotype is I^A I^B, producing gametes I^A or I^B.

Possible Children Blood Groups

Man (I^A i) produces gametes I^A or i. Cross with woman (I^A I^B):

	IA	IB
IA	IA IA (A)	IA IB (AB)
i	IA i (A)	i IB (B)

Offspring genotypes: I^A I^A (A), I^A i (A), I^A I^B (AB), I^B i (B). Distinct phenotypes: A, AB, B—three different blood groups.

Introduction: Unraveling Blood Group Inheritance Patterns

Blood group inheritance follows Mendelian genetics with codominance in the ABO system, crucial for CSIR NET Life Sciences. This article solves: A man whose mother and father had blood groups A and O respectively, marries a woman with blood group AB. If the man has blood group A, the number of different blood groups possible among their children.

Decoding Parental Genotypes Step-by-Step

• Father of man (O): Genotype ii (homozygous recessive).
• Mother of man (A): Must be I^A i (heterozygous), as she passed i to son alongside I^A from her.
• Man (A): Inherits I^A (mother) and i (father), so I^A i.
• Wife (AB): I^A I^B (codominant).

No options to “explain every option” as this is a fill-in-the-blank integer question, but common misconceptions include assuming 2 (A, B) or 4 groups—incorrect here due to man’s heterozygosity.

Punnett Square: Predicting Offspring Blood Groups

Visualize the cross (man I^A i × woman I^A I^B):

Gametes \ Parent	IA (woman)	IB (woman)
IA (man)	IA IA (A)	IA IB (AB)
i (man)	IA i (A)	IB i (B)

• A: From I^A I^A or I^A i.
• AB: From I^A I^B.
• B: From I^B i.
• O impossible (needs ii).

Thus, 3 different blood groups possible among children.

Importance for CSIR NET and Genetics Exams

This tests genotype deduction from pedigree and Punnett squares—key for molecular biology, genetics units. Practice similar: AB × O yields 2 (A, B); AA × AB yields 2 (A, AB).