Blood Types
Adapted from the Genetic Science Learning Center at The University of Utah website:
http://gslc.genetics.utah.edu/units/basics/blood/types.cfm
Background: The most common blood type classification system is the A-B-O
system discovered by Karl Landsteiner in the early 1900s. There are four blood
types in the ABO system: A, B, AB, and O.
Everybody inherits their blood type from their parents. You receive one
gene from your mother and one from your father, which combine to make your
blood genotype. The genes determine your blood type by causing surface proteins
(called agglutinogens) to exist on the surface of your red blood cells. Look at the
following diagram.
There are three different alleles: O, A, and B. If you inherit an O allele it
makes no surface protein, an A allele makes an “A” protein, and a B allele makes a
“B” protein. The A and B alleles are co-dominant (meaning both are dominant),
and the O allele is recessive. Just like other recessive genes, the O allele is
masked when paired with an A or a B. Since there are three different alleles, it
means there are six possible genotypes: AA, BB, OO, AB, AO, and BO. Using what
you’ve just learned, fill in the types in the chart below. (Refer to the diagram
above if needed.)
Blood Genotype
AA
AO
BB
BO
AB
OO
Blood Type (Phenotype)
Now that you have a little background on blood types, let’s investigate how blood
types are inherited by using Punnett Squares. Since blood type genetics involves
co-dominant genes, we need to make a little adjustment in how we use the Punnett
square. You will use all capital letters and need to remember that O is recessive.
Your teacher will walk you through this first example:
Sample Blood Type Punnett Square
Mom: genotype: AA
Dad: genotype: AO
Mom: phenotype _____ Dad: phenotype _____
Do any of the offspring have a blood type that is
different from their parent’s? _______ (yes/no)
Now, you try your hand….
A) Mom: genotype: AB
Mom: phenotype _____
Dad: genotype: BO
Dad: phenotype _____
Do any of the offspring have a blood type that is
different from their parent’s? _______ (yes/no)
B) Mom: genotype: AA
Dad: genotype: BB
Mom: phenotype _____ Dad: phenotype _____
Do any of the offspring have a blood type that is
different from their parent’s? _______ (yes/no)
C) Mom: genotype: AO
Mom: phenotype _____
Dad: genotype: OO
Dad: phenotype _____
Do any of the offspring have a blood type that is
different from their parent’s? _______ (yes/no)
Questions: (Use complete sentences.)
Explain how a child can receive a different blood type than either parent using
an example from one of your Punnett squares on the previous page.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
Now, apply what you’ve learned. Show your work using Punnett Squares.
3. Cross these two parents: AA x BO. What are the genotypes and phenotypes of
the children?
4. A mom with Type A blood, and a dad who is Type AB are expecting a child.
What are the possible genotypes and phenotypes of the kid? (Hint: you’ll need
to do 2 Punnett squares to cover all possible children.)
5. A mom has homozygous Type A blood, and a dad has heterozygous Type B
blood. Complete a Punnett square for this cross.
6. Jill is blood type O. She has two older brothers (who tease her like crazy) with
blood types A & B. What are the genotypes of her parents? (Hint: you’ll do this
Punnett square backwards… start with the children.)
Ready for a CSI challenge? Try this mystery… (or was it a crime?)
Mrs. Emma Black and Mrs. Bunny Walker shared a room at the hospital when they
had their babies, and now they suspect their babies have been accidentally
switched. The hospital says they did not make a mistake, but agreed to perform
blood tests to prove their innocence. Below are the results of those blood tests.
Begin your investigation by listing the possible genotypes for each person.
People
Mrs. Emma Black
Mr. Ernest Black
Mrs. Bunny Walker
Mr. Bob Walker
Baby #1
Baby #2
Blood
Type
A
AB
A
B
O
B
Possible
Genotype(s)
Next, using Punnett Squares, cross the married couples to prove which baby belongs
to which set of parents. Be a good scientist—the courts want to see evidence!
P1
P2
P3
P4
P5
P6
1. Which baby (#1 or #2) belongs to Mr. and Mrs. Black? ______ Which of your
Punnett Squares proves your answer? _______
2. Which baby (#1 or #2) belongs to Mr. and Mrs. Walker? ______ Which of
your Punnett Squares proves your answer? _______