Despite humanity's conflicts, there's a common saying that we all bleed the same blood. However, this is not entirely accurate.
Our blood contains different varieties distinguished by certain proteins known as antigens.
Hemoglobin
Red blood cells contain a protein called hemoglobin that binds to oxygen for transport throughout the body.
Antigens & Immune System
Red blood cells also have complex proteins called antigens on their surfaces.
Antigens communicate with white blood cells (immune cells) and help the immune system identify the body's own cells, preventing attacks on them as foreign bodies.
The two main antigens, A and B, determine blood type.
Genetics of Blood Types
Blood types are determined by three alleles of a gene: A, B, and O.
A and B Alleles: Code for A and B antigens respectively.
O Allele: Codes for neither A nor B antigen.
Inheritance: Each individual inherits one allele from each parent.
Dominance:
A and B alleles are dominant over O.
A x A = Type A
B x B = Type B
A x B = Type AB (Codominance)
O x O = Type O (Recessive)
A or B over O = Type A or B
Parental blood types help predict children's blood types.
Importance of Blood Types
Blood Transfusions
Correct blood matching is crucial for transfusions.
Mismatched blood transfusions (e.g., Type A given Type B) can cause the immune system to attack the foreign blood.
Universal Recipients: Type AB (accept all types)
Universal Donors: Type O (can donate to all types but can only receive Type O)
Rh Factor
Besides ABO system, Rh factor also matters (Rh+ or Rh- based on D antigen presence).
Rh incompatibility can cause complications in pregnancy (e.g., Rh- mother & Rh+ fetus —> hemolytic disease of the newborn).
Miscellaneous
Associations between blood type and personality are cultural and not scientifically proven.
The distribution of blood types varies by human population, but the evolutionary reasons are unclear (possibly for disease protection or genetic drift).
Different species have different antigen sets (e.g., dogs have 13 blood types).