Chromosome on ABO blood group is
**Core Concept**
The ABO blood group system is a crucial immunohematological system that determines an individual's blood type, which is determined by the presence or absence of specific antigens on the surface of red blood cells. This system is controlled by a single gene on a specific chromosome.
**Why the Correct Answer is Right**
The correct answer is related to the genetic basis of the ABO blood group system. The ABO blood group gene, also known as the ABO gene, is located on chromosome 9. This gene encodes for the enzyme fucosyltransferase, which is responsible for adding fucose molecules to the H antigen on the surface of red blood cells, resulting in the formation of A or B antigens. The presence or absence of this enzyme determines an individual's ABO blood group.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because chromosome 1 does not participate in the ABO blood group system.
**Option B:** Incorrect because chromosome 6 is associated with the major histocompatibility complex (MHC) genes, not the ABO blood group system.
**Option C:** Incorrect because chromosome 19 is associated with the ABO gene's regulatory elements, but not the gene itself.
**Clinical Pearl / High-Yield Fact**
The ABO blood group system is a key consideration in transfusion medicine, and understanding the genetic basis of this system is essential for ensuring safe blood transfusions. ABO incompatibility between donor and recipient can lead to severe hemolytic reactions.
**Correct Answer: C. 9**