Why do we have blood types?

Answer: Antigens on red blood cells vary

To identify family members — Wrong. Blood types aren't for identification. They exist because of genetic variations in antigens (protein markers) on red blood cell surfaces. Your immune system produces antibodies against antigens you don't have.

Antigens on red blood cells vary ✓ — Correct! Blood types (A, B, AB, O) are determined by antigens - protein markers on red blood cell surfaces. Type A has A antigens, B has B antigens, AB has both, and O has neither. Your immune system makes antibodies against antigens you lack. If incompatible blood is transfused, antibodies attack the foreign cells, causing dangerous clumping. The Rh factor is another antigen system.

Different oxygen capacities — Wrong. All blood types carry oxygen equally well using hemoglobin. Blood types differ because of genetic variations in surface antigens on red blood cells, which trigger immune responses if mixed incorrectly.