True regarding blood group A
**Core Concept**
The ABO blood group system is a fundamental concept in transfusion medicine, which categorizes blood into different groups based on the presence or absence of specific antigens on the surface of red blood cells. The ABO blood group system is determined by a single gene with three alleles: A, B, and O.
**Why the Correct Answer is Right**
Blood group A is determined by the presence of A antigen on the surface of red blood cells. This antigen is encoded by the A gene, which is a glycosyltransferase enzyme responsible for adding N-acetylgalactosamine to the H antigen on the red blood cell membrane. The A antigen is recognized by antibodies in people with blood groups B, AB, and O, making them incompatible for blood transfusions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the characteristic of blood group A.
**Option B:** This option is incorrect because it is a characteristic of blood group B, not A.
**Option C:** This option is incorrect because it is a characteristic of blood group O, not A.
**Clinical Pearl / High-Yield Fact**
In the ABO blood group system, individuals with blood group A can receive blood from individuals with blood groups A and O, but not from individuals with blood groups B or AB.
**Correct Answer:** B. The A antigen is encoded by the A gene, a glycosyltransferase enzyme.