2. A mother of blood group O has a group A child. The father could be of blood type
(1) A or B or O.       (2) A only.
(3) A or AB.            (4) AB only.

Genetic reasoning

ABO alleles

• I^AI^A: A
• I^BI^B: B
• ii: O [web:119][web:123]

Blood group analysis

Blood group O phenotype = genotype ii.

Mother is ii → passes only i to child.

Blood group A child = genotypes I^AI^A or I^Ai.

Since mother contributes i, child must be I^Ai.

Father’s contribution

Father must supply I^A allele [web:120].

Possible father phenotypes

• Type A: I^AI^A or I^Ai → can pass I^A
• Type AB: I^AI^B → can pass I^A
• Type B: I^BI^B or I^Bi → no I^A
• Type O: ii → no I^A

Father can be A or AB only [web:122].

Option-wise evaluation

• A or B or O: incorrect – B and O cannot provide I^A
• A only: incomplete – excludes AB
• A or AB: correct
• AB only: too restrictive – excludes type A

Thus, with type O mother and type A child, father could be blood group A or AB [web:126].