Inheritance pattern of ABO blood group system is –
**Core Concept**
The ABO blood group system is a classic example of a polymorphic genetic trait, where the genetic variation affects the carbohydrate structure of the red blood cell surface. This variation is determined by a single gene (ABO) with three alleles (A, B, and O) that code for different enzymes involved in the synthesis of ABO antigens.
**Why the Correct Answer is Right**
The correct answer is based on the principle of Mendelian genetics, where the ABO gene has three alleles: A, B, and O. The O allele is recessive, while the A and B alleles are codominant. The possible genotypes and phenotypes are:
- AA or AO: A blood group
- BB or BO: B blood group
- AB: AB blood group
- OO: O blood group
The ABO blood group system follows an autosomal codominant pattern, meaning that both A and B alleles are expressed when present together.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the ABO blood group system is not an autosomal recessive trait, as it does not follow a simple recessive-dominant pattern.
**Option B:** Incorrect because the ABO blood group system is not X-linked, as it is inherited in an autosomal pattern.
**Option C:** Incorrect because the ABO blood group system is not a polygenic trait, as it is determined by a single gene with multiple alleles.
**Clinical Pearl / High-Yield Fact**
The ABO blood group system is clinically significant because it determines the risk of hemolytic disease of the newborn (HDN) and transfusion reactions. Understanding the inheritance pattern of ABO blood groups is essential for blood banking and transfusion medicine.
**Correct Answer: D. Autosomal codominant.**