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.
In your notebook, copy and complete the chart below. (Hint: Look at the diagram above.)
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.
E. Gratkins, Smith JH
Page 1 of 2, rev. 2/7/16
Your teacher will walk you through this first example.
Let’s try these parents…
1.
2.
3.
4.
Mom - genotype is AA
Dad - genotype is AO
What phenotypes do Mom and Dad have?
Create a Punnett square for the cross.
What are the offspring possibilities?
Do the children match the blood type of one of the parents? Explain why or why not.
Now, it’s your turn…. (show work in your notebook – as modeled in class)
A)
Mom - genotype is AB
Dad - genotype is BO
B)
Mom - genotype is AA
Dad - genotype is BB
C)
Mom - genotype is AO
Dad - genotype is OO
Questions: Answer these in your notebook. Show your work using Punnett Squares.
1. Cross these two parents: AA x BO. What are the genotypes and phenotypes of the children?
2. 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? (You’ll need more than 1 Punnett square here.)
3. A mom has homozygous Type A blood, and a dad has heterozygous Type B blood. Complete
a Punnett square for this cross.
4. 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: do this Punnett square backwards…
start with the kids.)
5. Explain how a child can receive a different blood type than either parent using an example
from one of your Punnett squares.
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.
People
Mrs. Emma Black
Mr. Ernest Black
Mrs. Bunny Walker
Mr. Bob Walker
Baby #1
Baby #2
Blood Type
(Phenotype)
A
AB
A
B
O
B
Using Punnett Squares, cross the married couples to
prove which baby belongs to which set of parents.
(Hint: you’ll have to know the genotypes first.)
Be a good scientist—the courts want to see
evidence!
E. Gratkins, Smith JH
Page 2 of 2, rev. 2/7/16
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