What is the phenotypic ratio of the offspring when a man who has type A blood, and whose mother had type O blood, marries a woman who has type AB blood? 2 type A : 1 type AB : 1 type B
3 type A: 1 type B
1 type A : 1 type O
1AA :1AB : 1AO : 1BO

The correct answer is - 2 type A : 1 type AB : 1 type B

Explanation:

The pattern of the inheritance in the ABO blood group system is the example of the multiple alleles and codominance. There are three alleles in this sytem that determines what blood group would be in an indvidual that are; IA, IB, and IO. The allele IO is a recessive allele to both IA, and IB alleles whereas IA and IB are show codominance when present in heterzygous condition.

Genotype of a person with “A” blood group can be IA IO  or IA IA but as it is given that the mother of the male with A bglood group is O blood group which means there must be a IO allele would be present in the male too so the genotype would be IAIO.

The genotype of AB blood group mother would be IAIB as shows codominance. so the cross between these woulde be as follows:

IA IO  x IA IB

Gametes :

IA  IO , and IA  IB

  IA       IO

IA    IAIA    IAIO

IB    IAIB    IBIO

phenotypic ratio = 2 A group : 1 AB group : 1 B group