25-30 minutes

Genetics Basics: Blood Types & Matching

Explore how blood types are inherited and why matching matters for transfusions and transplants.

Learning Objectives

Explain how blood types are determined by genetics (inheritance patterns)
Understand why blood type matching is important for transfusions
Introduce the concept that other genetic factors (like HLA) affect matching for transplants

Materials

Whiteboard for Punnett squares
Blood type compatibility chart (can draw on board)
Note-taking materials

Lesson Content

Introduction: What Determines Blood Type? (5 min)

"Your blood type is determined by your genes—inherited from your parents."
"There are three alleles for blood type: A, B, and O."
"A and B are codominant (both expressed if present), while O is recessive."
"You inherit one allele from each parent, giving you two alleles that determine your type."

Blood Type Combinations (8-10 min)

Compatibility table below adapted from American Red Cross and NIH MedlinePlus standard blood-type references.

Genotype	Blood Type	Can Donate To	Can Receive From
AA or AO	Type A	A, AB	A, O
BB or BO	Type B	B, AB	B, O
AB	Type AB	AB only	All types
OO	Type O	All types	O only

"Type O is called the 'universal donor'—can give to anyone."
"Type AB is called the 'universal recipient'—can receive from anyone."
"The Rh factor adds another layer: you're either positive (+) or negative (-)."

Why Matching Matters (5 min)

"If you receive the wrong blood type, your immune system attacks the foreign cells."
"Antigens on the red blood cells trigger antibodies in the recipient's plasma."
"This is why hospitals always test blood type before transfusions."
"For blood transfusions, matching is relatively straightforward with 8 common types."

Beyond Blood Type: HLA Matching (5 min)

"For bone marrow or stem cell transplants, matching is much more complex."
"Instead of just blood type, doctors look at HLA markers—Human Leukocyte Antigens."
"There are thousands of possible HLA combinations, not just 8 like blood types (Source: IPD-IMGT/HLA Database)."
"People who share ancestry are more likely to have similar HLA types (Source: NMDP / Be The Match)."
"This is why diverse donor registries are so important—more variety means more matches."

Closing (2 min)

"Blood types show us how genetics directly affects our health and medical care."
"Next lesson, we'll explore how donor registries help connect patients with matching donors."

Activity: Punnett Square Practice

Problem-Solving Scenario:

A hospital has a patient with Type B blood who needs a transfusion. The available donors are: Parent A (Type AB), Parent B (Type O), Child 1 (Type A), Child 2 (Type B).

Which donor(s) can give blood to the patient? Why?
Use a Punnett square: If Parent A (AB) and Parent B (OO) have children, what are the possible blood types?
Discussion: Could Child 1 (Type A) and Child 2 (Type B) be children of Parents A and B? Explain.

Blood Type: A classification of blood based on the presence or absence of certain antigens on red blood cells (A, B, AB, or O).
Allele: A version of a gene; you inherit one allele from each parent.
Dominant: An allele that is expressed (shows up) when at least one copy is present.
Recessive: An allele that is only expressed when two copies are present (one from each parent).
Rh Factor: A protein on red blood cells; if present, blood is Rh positive (+), if absent, Rh negative (-).
Transfusion: The transfer of blood from one person (donor) to another (recipient).

Discussion Questions

Why is Type O called the "universal donor"? What makes it special?
If blood type matching is relatively simple, why is bone marrow matching so much harder?
How might your ancestry affect your ability to find a bone marrow match?

Optional Extension

Research the history of blood transfusions. When were blood types discovered? What happened before doctors understood blood type matching?