Blood Types

Giving the Gift of Life

• Blood type is crucial for safe blood transfusions.
• Different individuals inherit different blood types, affecting which blood types they can receive.

What Are Blood Types?

Definition

• Blood type: Genetic trait based on presence/absence of antigens on red blood cells.
• Blood group system: Includes all genes, alleles, genotypes, and phenotypes for a set of blood type antigens.
• Notable systems: ABO and Rhesus (Rh), with 33 other less-known systems.

Antigens and Antibodies

• Antigens: Molecules on cells recognized as self or non-self by the immune system.
  • Can be proteins, carbohydrates, glycoproteins, or glycolipids.
• Antibodies: Y-shaped proteins targeting non-self antigens, marking them for immune response.
• Antigens on pathogens or transfused blood can trigger antibody production.

Genetics of Blood Type

• Blood type is inherited through alleles from parents.
• Typically controlled by single genes or closely linked genes.
• Rare cases of blood type changes (e.g., bone marrow transplants).

ABO Blood Group System

Antigens

• Antigens in ABO system are glycoproteins.
• Four blood types:
  1. Type A: Only A antigen.
  2. Type B: Only B antigen.
  3. Type AB: Both A and B antigens.
  4. Type O: Neither antigen.

Genetics

• Controlled by a gene on chromosome 9 with three alleles: IA, IB, and i.
• Six genotypes leading to four phenotypes:
  • IAi or IAIA: Type A
  • IBi or IBIB: Type B
  • IAIB: Type AB
  • ii: Type O
• Codominance: IA and IB are dominant over i and codominant with each other.

Medical Significance

• ABO compatibility is critical in transfusions to avoid immune response and hemolytic reactions.
• Type O: Universal donor (can give to any type).
• Type AB: Universal recipient (can receive from any type).

Rhesus Blood Group System

Overview

• Rhesus system includes multiple antigens, mainly D antigen.
• Rh+ has D antigen, Rh- lacks it.
• Controlled by two genes on chromosome 1, affecting ion transport.

Transfusions

• Rh+ can receive both Rh+ and Rh- blood.
• Rh- can only receive Rh- blood.
• Anti-D antibodies form upon exposure to Rh+ blood, not naturally present.

Hemolytic Disease of the Newborn

• Occurs if Rh- mother carries an Rh+ fetus and has anti-D antibodies from previous pregnancy.
• Prevented by Rho(D) immune globulin injection to mother.

Myth vs. Reality

• Myth: Blood type determines dietary needs and personality traits.
• Reality: No scientific basis for these claims; considered pseudoscience.

Review Questions

1. Define blood type and blood group system.
2. Explain antigens and antibodies relationship.
3. Describe ABO alleles, genotypes, and phenotypes.
4. Discuss ABO system's medical significance.
5. Explain ABO blood types' disease susceptibility.
6. Describe Rhesus system.
7. Relate Rhesus system to transfusions.
8. Causes of hemolytic disease of the newborn.