In clinical medicine, understanding ABO blood group inheritance is essential for safe bloo… — JAMB UTME

In clinical medicine, understanding ABO blood group inheritance is essential for safe blood transfusions. A patient with blood group O requires a blood transfusion. Which of the following genotypes must a donor possess to ensure that their red blood cells express neither A nor B surface antigens?

$ii$ Answer
B
$I^A I^B$
C
$I^A i$
D
$I^B i$

Answer

The donor must possess the homozygous recessive genotype

ii

The allele

i

is recessive to both codominant alleles

I^A

and

I^B

. Therefore, an individual must be homozygous recessive with genotype

ii

to have blood group O, which lacks both A and B surface antigens on red blood cells.

Step-by-Step Solution

Identify the genetic basis of blood group O

Blood group O red blood cells lack both A and B agglutinogens (antigens).

The production of surface antigens is controlled by the

I^A

I^B

, and

i

alleles.

Determine the allele dominance relationship

Alleles

I^A

and

I^B

are codominant with respect to each other, and both are completely dominant over allele

i

Allele

i

is a recessive allele that does not code for any functional surface antigen enzyme.

Select the genotype producing no antigens

Only individuals who are homozygous recessive (

ii

) express neither antigen.

Individuals with genotype

ii

belong to blood group O, making their un-agglutinated cells safe for recipients requiring antigen-free donor blood.

Key Concept

ABO blood group genetics and medical application in transfusion safety

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