Question

In simple Mendelian inheritance alleles display a simple dominant/recessive relationship. There are many exceptions to Mendelian laws of inheritance. Most genes have more than two allelic forms and do not exhibit simple Mendelian inheritance. The human ABO antigens are an example of a multiple allelic trait. There are three ABO blood group antigens, IA, IB and i. The i allele is recessive to both IA and IB. A person who is homozygous ii has type O blood and does not produce either the IA or IB antigens. A homozygous IAIA or heterozygous IAi individual has type A blood. Similarly, a homozygous IBIB or heterozygous IBi individual produces surface antigen B. A person who is IAIB has the blood type AB and expresses both surface antigens A and B as the IA and IB alleles are codominant to each other.

1) A child with blood type O is born to a mother with type A blood. What is the genotype of the child?

A) IAIB

B)IAi

C)IBIB

D)IAIA

E)ii

Answer 1

The answer is option E

Reason: For a person to get O blood group he/she need to have homozygous “ii”. So irrespective of the mothers blood group the child must have homozygous “ii” . For this the mother must compulsory possess the genotype of heterozygous A blood group i.e “ IAi ”. If not so the child cannot get O blood group and the father can be either homozygous to O blood group i.e “ii” or heterozygous to A or B blood gropus i.e “IAi” , “IBi” respectively.